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In vector calculus, the Jacobian matrix (/dʒəˈkoʊbiən/,^[1]^[2]^[3]/dʒɪ-, jɪ-/) is the matrix of all first-order partial derivatives of a vector-valued function. When the matrix is a square matrix, both the matrix and its determinant are referred to as the Jacobian in literature.^[4]

Suppose $f : ℝ n \to ℝ m$ is a function which takes as input the vector $x \in ℝ n$ and produces as output the vector $f (x) \in ℝ m$ . Then the Jacobian matrix $J$ of $f$ is an $m \times n$ matrix, usually defined and arranged as follows:

{displaystyle mathbf {J} ={begin{bmatrix}{dfrac {partial mathbf {f} }{partial x_{1}}}&cdots &{dfrac {partial mathbf {f} }{partial x_{n}}}end{bmatrix}}={begin{bmatrix}{dfrac {partial f_{1}}{partial x_{1}}}&cdots &{dfrac {partial f_{1}}{partial x_{n}}}\vdots &ddots &vdots \{dfrac {partial f_{m}}{partial x_{1}}}&cdots &{dfrac {partial f_{m}}{partial x_{n}}}end{bmatrix}}}

or, component-wise:

{displaystyle mathbf {J} _{ij}={frac {partial f_{i}}{partial x_{j}}}.}

This matrix, whose entries are functions of $x$ , is also denoted by $D f$ , $J f$ , and ∂(f₁,...,f_m)/∂(x₁,...,x_n). (Note that some literature defines the Jacobian as the transpose of the matrix given above.)

The Jacobian matrix is important because if the function $f$ is differentiable at a point $x$ (this is a slightly stronger condition than merely requiring that all partial derivatives exist at $x$ ), then the Jacobian matrix defines a linear map $ℝ n \to ℝ m$ , which is the best (pointwise) linear approximation of the function $f$ near the point $x$ . This linear map is thus the generalization of the usual notion of derivative, and is called the derivative or the differential of $f$ at $x$ .

If $m$ = $n$ , the Jacobian matrix is a square matrix, and its determinant, a function of $x 1, \dots, x n$ , is the Jacobian determinant of $f$ . It carries important information about the local behavior of $f$ . In particular, the function $f$ has locally in the neighborhood of a point $x$ an inverse function that is differentiable if and only if the Jacobian determinant is nonzero at $x$ (see Jacobian conjecture). The Jacobian determinant also appears when changing the variables in multiple integrals (see substitution rule for multiple variables).

If $m$ = 1, $f$ is a scalar field and the Jacobian matrix is reduced to a row vector of partial derivatives of $f$ —i.e. the transpose of the gradient of $f$ , when denoted as column vector with respect to the ordered basis ${displaystyle {{hat {mathbf {x} }}_{1},cdots ,{hat {mathbf {x} }}_{n}}}$ .

These concepts are named after the mathematician Carl Gustav Jacob Jacobi (1804–1851).

Jacobian matrix

The Jacobian generalizes the gradient of a scalar-valued function of multiple variables, which itself generalizes the derivative of a scalar-valued function of a single variable. In other words, the Jacobian for a scalar-valued multivariate function is the gradient and that of a scalar-valued function of single variable is simply its derivative. The Jacobian can also be thought of as describing the amount of "stretching", "rotating" or "transforming" that a transformation imposes locally. For example, if $(x', y') = f (x, y)$ is used to transform an image, the Jacobian $J f (x, y)$ , describes how the image in the neighborhood of $(x, y)$ is transformed.

If a function is differentiable at a point, its derivative is given in coordinates by the Jacobian, but a function does not need to be differentiable for the Jacobian to be defined, since only the partial derivatives are required to exist.

If $p$ is a point in $ℝ n$ and $f$ is differentiable at $p$ , then its derivative is given by $J f (p)$ . In this case, the linear map described by $J f (p)$ is the best linear approximation of $f$ near the point $p$ , in the sense that

mathbf {f} (mathbf {x} )=mathbf {f} (mathbf {p} )+mathbf {J} _{mathbf {f} }(mathbf {p} )(mathbf {x} -mathbf {p} )+o(|mathbf {x} -mathbf {p} |)

for $x$ close to $p$ and where $o$ is the little o-notation (for $x \to p$ ) and $‖ x - p ‖$ is the distance between $x$ and $p$ . (See Total derivative#The total derivative as a linear map.)

Compare this to a Taylor series for a scalar function of a scalar argument, truncated to first order:

f(x)=f(p)+f'(p)(x-p)+o(x-p).

In a sense, both the gradient and Jacobian are "first derivatives"—the former the first derivative of a scalar function of several variables, the latter the first derivative of a vector function of several variables.

The Jacobian of the gradient of a scalar function of several variables has a special name: the Hessian matrix, which in a sense is the "second derivative" of the function in question.

Jacobian determinant

A nonlinear map

{displaystyle fcolon mathbb {R} ^{2}to mathbb {R} ^{2}}

sends a small square (left, in red) to a distorted parallelogram (right, in red). The Jacobian at a point gives the best linear approximation of the distorted parallelogram near that point (right, in translucent white), and the Jacobian determinant gives the ratio of the area of the approximating parallelogram to that of the original square.

If $m = n$ , then $f$ is a function from $ℝ n$ to itself and the Jacobian matrix is a square matrix. We can then form its determinant, known as the Jacobian determinant. The Jacobian determinant is sometimes referred to as "the Jacobian".

The Jacobian determinant at a given point gives important information about the behavior of $f$ near that point. For instance, the continuously differentiable function $f$ is invertible near a point $p \in ℝ n$ if the Jacobian determinant at $p$ is non-zero. This is the inverse function theorem. Furthermore, if the Jacobian determinant at $p$ is positive, then $f$ preserves orientation near $p$ ; if it is negative, $f$ reverses orientation. The absolute value of the Jacobian determinant at $p$ gives us the factor by which the function $f$ expands or shrinks volumes near $p$ ; this is why it occurs in the general substitution rule.

The Jacobian determinant is used when making a change of variables when evaluating a multiple integral of a function over a region within its domain. To accommodate for the change of coordinates the magnitude of the Jacobian determinant arises as a multiplicative factor within the integral. This is because the $n$ -dimensional $dV$ element is in general a parallelepiped in the new coordinate system, and the $n$ -volume of a parallelepiped is the determinant of its edge vectors.

The Jacobian can also be used to solve systems of differential equations at an equilibrium point or approximate solutions near an equilibrium point.

Inverse

According to the inverse function theorem, the matrix inverse of the Jacobian matrix of an invertible function is the Jacobian matrix of the inverse function. That is, if the Jacobian of the function $f : ℝ n \to ℝ n$ is continuous and nonsingular at the point $p$ in $ℝ n$ , then $f$ is invertible when restricted to some neighborhood of $p$ and

mathbf {J} _{mathbf {f} ^{-1}}circ mathbf {f} ={mathbf {J} _{mathbf {f} }}^{-1}.

Conversely, if the Jacobian determinant is not zero at a point, then the function is locally invertible near this point, that is, there is a neighbourhood of this point in which the function is invertible.

The (unproved) Jacobian conjecture is related to global invertibility in the case of a polynomial function, that is a function defined by n polynomials in n variables. It asserts that, if the Jacobian determinant is a non-zero constant (or, equivalently, that it does not have any complex zero), then the function is invertible and its inverse is a polynomial function.

Critical points

If $f : ℝ n \to ℝ m$ is a differentiable function, a critical point of $f$ is a point where the rank of the Jacobian matrix is not maximal. This means that the rank at the critical point is lower than the rank at some neighbour point. In other words, let $k$ be the maximal dimension of the open balls contained in the image of $f$ ; then a point is critical if all minors of rank $k$ of $f$ are zero.

In the case where $1 = m = n = k$ , a point is critical if the Jacobian determinant is zero.

Examples

Example 1

Consider the function $f : ℝ 2 \to ℝ 2,$ with $(x, y) \mapsto (f 1 (x, y), f 2 (x, y)),$ given by

{displaystyle mathbf {f} ({begin{bmatrix}x\yend{bmatrix}})={begin{bmatrix}f_{1}(x,y)\f_{2}(x,y)end{bmatrix}}={begin{bmatrix}x^{2}y\5x+sin yend{bmatrix}}.}

Then we have

f_{1}(x,y)=x^{2}y

and

f_{2}(x,y)=5x+sin y

and the Jacobian matrix of $f$ is

mathbf {J} _{mathbf {f} }(x,y)={begin{bmatrix}{dfrac {partial f_{1}}{partial x}}&{dfrac {partial f_{1}}{partial y}}\[1em]{dfrac {partial f_{2}}{partial x}}&{dfrac {partial f_{2}}{partial y}}end{bmatrix}}={begin{bmatrix}2xy&x^{2}\5&cos yend{bmatrix}}

and the Jacobian determinant is

det(mathbf {J} _{mathbf {f} }(x,y))=2xycos y-5x^{2}.

Example 2: polar-Cartesian transformation

The transformation from polar coordinates $(r, φ)$ to Cartesian coordinates (x, y), is given by the function $F : ℝ + \times [0, 2 π) \to ℝ 2$ with components:

{begin{aligned}x&=rcos varphi ;\y&=rsin varphi .end{aligned}}

{displaystyle mathbf {J} _{mathbf {F} }(r,varphi )={begin{bmatrix}{dfrac {partial x}{partial r}}&{dfrac {partial x}{partial varphi }}\[1em]{dfrac {partial y}{partial r}}&{dfrac {partial y}{partial varphi }}end{bmatrix}}={begin{bmatrix}cos varphi &-rsin varphi \sin varphi &rcos varphi end{bmatrix}}}

The Jacobian determinant is equal to $r$ . This can be used to transform integrals between the two coordinate systems:

{displaystyle iint _{mathbf {F} (A)}f(x,y),dx,dy=iint _{A}f(rcos varphi ,rsin varphi ),r,dr,dvarphi .}

Example 3: spherical-Cartesian transformation

The transformation from spherical coordinates $(r, θ, φ)$ to Cartesian coordinates (x, y, z), is given by the function $F : ℝ + \times [0, π] \times [0, 2 π) \to ℝ 3$ with components:

{begin{aligned}x&=rsin theta cos varphi ;\y&=rsin theta sin varphi ;\z&=rcos theta .end{aligned}}

The Jacobian matrix for this coordinate change is

mathbf {J} _{mathbf {F} }(r,theta ,varphi )={begin{bmatrix}{dfrac {partial x}{partial r}}&{dfrac {partial x}{partial theta }}&{dfrac {partial x}{partial varphi }}\[1em]{dfrac {partial y}{partial r}}&{dfrac {partial y}{partial theta }}&{dfrac {partial y}{partial varphi }}\[1em]{dfrac {partial z}{partial r}}&{dfrac {partial z}{partial theta }}&{dfrac {partial z}{partial varphi }}end{bmatrix}}={begin{bmatrix}sin theta cos varphi &rcos theta cos varphi &-rsin theta sin varphi \sin theta sin varphi &rcos theta sin varphi &rsin theta cos varphi \cos theta &-rsin theta &0end{bmatrix}}.

The determinant is $r 2 sin θ$ . As an example, since $dV = dx dy dz$ this determinant implies that the differential volume element $dV = r 2 sin θ dr dθ dφ$ . Unlike for a change of Cartesian coordinates, this determinant is not a constant, and varies with coordinates ( $r$ and $θ$ ).

Example 4

The Jacobian matrix of the function $F : ℝ 3 \to ℝ 4$ with components

{begin{aligned}y_{1}&=x_{1}\y_{2}&=5x_{3}\y_{3}&=4x_{2}^{2}-2x_{3}\y_{4}&=x_{3}sin x_{1}end{aligned}}

is

mathbf {J} _{mathbf {F} }(x_{1},x_{2},x_{3})={begin{bmatrix}{dfrac {partial y_{1}}{partial x_{1}}}&{dfrac {partial y_{1}}{partial x_{2}}}&{dfrac {partial y_{1}}{partial x_{3}}}\[1em]{dfrac {partial y_{2}}{partial x_{1}}}&{dfrac {partial y_{2}}{partial x_{2}}}&{dfrac {partial y_{2}}{partial x_{3}}}\[1em]{dfrac {partial y_{3}}{partial x_{1}}}&{dfrac {partial y_{3}}{partial x_{2}}}&{dfrac {partial y_{3}}{partial x_{3}}}\[1em]{dfrac {partial y_{4}}{partial x_{1}}}&{dfrac {partial y_{4}}{partial x_{2}}}&{dfrac {partial y_{4}}{partial x_{3}}}end{bmatrix}}={begin{bmatrix}1&0&0\0&0&5\0&8x_{2}&-2\x_{3}cos x_{1}&0&sin x_{1}end{bmatrix}}.

This example shows that the Jacobian need not be a square matrix.

Example 5

The Jacobian determinant of the function $F : ℝ 3 \to ℝ 3$ with components

{begin{aligned}y_{1}&=5x_{2}\y_{2}&=4x_{1}^{2}-2sin(x_{2}x_{3})\y_{3}&=x_{2}x_{3}end{aligned}}

is

{begin{vmatrix}0&5&0\8x_{1}&-2x_{3}cos(x_{2}x_{3})&-2x_{2}cos(x_{2}x_{3})\0&x_{3}&x_{2}end{vmatrix}}=-8x_{1}{begin{vmatrix}5&0\x_{3}&x_{2}end{vmatrix}}=-40x_{1}x_{2}.

From this we see that $F$ reverses orientation near those points where $x 1$ and $x 2$ have the same sign; the function is locally invertible everywhere except near points where $x 1 = 0$ or $x 2 = 0$ . Intuitively, if one starts with a tiny object around the point $(1, 2, 3)$ and apply $F$ to that object, one will get a resulting object with approximately $40 \times 1 \times 2 = 80$ times the volume of the original one, with orientation reversed.

Other uses

The Jacobian serves as a linearized design matrix in statistical regression and curve fitting; see non-linear least squares.

Dynamical systems

Consider a dynamical system of the form ${dot {{mathbf {x}}}}=F({mathbf {x}})$ , where ${dot {{mathbf {x}}}}$ is the (component-wise) derivative of $mathbf {x}$ with respect to the evolution parameter $t$ (time), and ${displaystyle Fcolon mathbb {R} ^{n}to mathbb {R} ^{n}}$ is differentiable. If ${displaystyle F(mathbf {x} _{0})=0}$ , then $mathbf{x}_{0}$ is a stationary point (also called a steady state). By the Hartman–Grobman theorem, the behavior of the system near a stationary point is related to the eigenvalues of ${displaystyle mathbf {J} _{F}left(mathbf {x} _{0}right)}$ , the Jacobian of $F$ at the stationary point.^[5] Specifically, if the eigenvalues all have real parts that are negative, then the system is stable near the stationary point, if any eigenvalue has a real part that is positive, then the point is unstable. If the largest real part of the eigenvalues is zero, the Jacobian matrix does not allow for an evaluation of the stability.^[6]

Newton's method

A square system of coupled nonlinear equations can be solved iteratively by Newton's method. This method uses the Jacobian matrix of the system of equations.

Surface analysis

Let n = 2 so the Jacobian is a 2 × 2 real matrix. Suppose a surface diffeomorphism f: U → V in the neighborhood of p in U is written ${displaystyle (u(x,y), v(x,y)).}$ The matrix ${displaystyle mathbf {J} _{mathbf {f} }(mathbf {p} )}$ can be interpreted as a complex number: ordinary, split, or dual. Furthermore, since ${displaystyle mathbf {J} _{mathbf {f} }(mathbf {p} )}$ is invertible, the complex number has a polar decomposition or an alternative planar decomposition.

And again, each such complex number represents a group action on the tangent plane at p. The action is dilation by the norm of the complex number, and rotation respecting angle, hyperbolic angle, or slope, according to the case of ${displaystyle mathbf {J} _{mathbf {f} }(mathbf {p} ).}$ Such action corresponds to a conformal mapping.

References

^ "Jacobian - Definition of Jacobian in English by Oxford Dictionaries". Oxford Dictionaries - English. Archived from the original on 1 December 2017. Retrieved 2 May 2018..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}

^ "the definition of jacobian". Dictionary.com. Archived from the original on 1 December 2017. Retrieved 2 May 2018.

^ Team, Forvo. "Jacobian pronunciation: How to pronounce Jacobian in English". forvo.com. Retrieved 2 May 2018.

^ W., Weisstein, Eric. "Jacobian". mathworld.wolfram.com. Archived from the original on 3 November 2017. Retrieved 2 May 2018.

^ Arrowsmith, D. K.; Place, C. M. (1992). "The Linearization Theorem". Dynamical Systems: Differential Equations, Maps, and Chaotic Behaviour. London: Chapman & Hall. pp. 77–81. ISBN 0-412-39080-9.

^ Hirsch, Morris; Smale, Stephen (1974). Differential equations, dynamical systems and linear algebra.

External links

Hazewinkel, Michiel, ed. (2001) [1994], "Jacobian", Encyclopedia of Mathematics, Springer Science+Business Media B.V. / Kluwer Academic Publishers, ISBN 978-1-55608-010-4

Mathworld A more technical explanation of Jacobians

[1] "Jacobian - Definition of Jacobian in English by Oxford Dictionaries". Oxford Dictionaries - English. Archived from the original on 1 December 2017. Retrieved 2 May 2018..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}

[2] "the definition of jacobian". Dictionary.com. Archived from the original on 1 December 2017. Retrieved 2 May 2018.

[3] Team, Forvo. "Jacobian pronunciation: How to pronounce Jacobian in English". forvo.com. Retrieved 2 May 2018.

[4] W., Weisstein, Eric. "Jacobian". mathworld.wolfram.com. Archived from the original on 3 November 2017. Retrieved 2 May 2018.

[5] Arrowsmith, D. K.; Place, C. M. (1992). "The Linearization Theorem". Dynamical Systems: Differential Equations, Maps, and Chaotic Behaviour. London: Chapman & Hall. pp. 77–81. ISBN 0-412-39080-9.

[6] Hirsch, Morris; Smale, Stephen (1974). Differential equations, dynamical systems and linear algebra.

v t e Matrix classes
Explicitly constrained entries	(0,1) Alternant Anti-diagonal Anti-Hermitian Anti-symmetric Arrowhead Band Bidiagonal Binary Bisymmetric Block-diagonal Block Block tridiagonal Boolean Cauchy Centrosymmetric Conference Complex Hadamard Copositive Diagonally dominant Diagonal Discrete Fourier Transform Elementary Equivalent Frobenius Generalized permutation Hadamard Hankel Hermitian Hessenberg Hollow Integer Logical Markov Metzler Monomial Moore Nonnegative Partitioned Parisi Pentadiagonal Permutation Persymmetric Polynomial Positive Quaternionic Sign Signature Skew-Hermitian Skew-symmetric Skyline Sparse Sylvester Symmetric Toeplitz Triangular Tridiagonal Unitary Vandermonde Walsh Z
Constant	Exchange Hilbert Identity Lehmer Of ones Pascal Pauli Redheffer Shift Zero
Conditions on eigenvalues or eigenvectors	Companion Convergent Defective Diagonalizable Hurwitz Positive-definite Stability Stieltjes
Satisfying conditions on products or inverses	Congruent Idempotent or Projection Invertible Involutory Nilpotent Normal Orthogonal Orthonormal Singular Unimodular Unipotent Totally unimodular Weighing
With specific applications	Adjugate Alternating sign Augmented Bézout Carleman Cartan Circulant Cofactor Commutation Coxeter Derogatory Distance Duplication Elimination Euclidean distance Fundamental (linear differential equation) Generator Gramian Hessian Householder Jacobian Moment Payoff Pick Random Rotation Seifert Shear Similarity Symplectic Totally positive Transformation Wedderburn X–Y–Z
Used in statistics	Bernoulli Centering Correlation Covariance Design Dispersion Doubly stochastic Fisher information Hat Precision Stochastic Transition
Used in graph theory	Adjacency Biadjacency Degree Edmonds Incidence Laplacian Seidel adjacency Skew-adjacency Tutte
Used in science and engineering	Cabibbo–Kobayashi–Maskawa Density Fundamental (computer vision) Fuzzy associative Gamma Gell-Mann Hamiltonian Irregular Overlap S State transition Substitution Z (chemistry)
Related terms	Jordan canonical form Linear independence Matrix exponential Matrix representation of conic sections Perfect matrix Pseudoinverse Quaternionic matrix Row echelon form Wronskian
List of matrices Category:Matrices

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