Calculus functions

sage.calculus.functions.jacobian(functions, variables)

Return the Jacobian matrix, which is the matrix of partial derivatives in which the i,j entry of the Jacobian matrix is the partial derivative diff(functions[i], variables[j]).

EXAMPLES:

sage: x,y = var('x,y')
sage: g=x^2-2*x*y
sage: jacobian(g, (x,y))
[2*x - 2*y      -2*x]

The Jacobian of the Jacobian should give us the “second derivative”, which is the Hessian matrix:

sage: jacobian(jacobian(g, (x,y)), (x,y))
[ 2 -2]
[-2  0]
sage: g.hessian()
[ 2 -2]
[-2  0]

sage: f=(x^3*sin(y), cos(x)*sin(y), exp(x))
sage: jacobian(f, (x,y))
[  3*x^2*sin(y)     x^3*cos(y)]
[-sin(x)*sin(y)  cos(x)*cos(y)]
[           e^x              0]
sage: jacobian(f, (y,x))
[    x^3*cos(y)   3*x^2*sin(y)]
[ cos(x)*cos(y) -sin(x)*sin(y)]
[             0            e^x]
sage.calculus.functions.wronskian(*args)

Returns the Wronskian of the provided functions, differentiating with respect to the given variable. If no variable is provided, diff(f) is called for each function f.

wronskian(f1,…,fn, x) returns the Wronskian of f1,…,fn, with derivatives taken with respect to x.

wronskian(f1,…,fn) returns the Wronskian of f1,…,fn where k’th derivatives are computed by doing .derivative(k) on each function.

The Wronskian of a list of functions is a determinant of derivatives. The nth row (starting from 0) is a list of the nth derivatives of the given functions.

For two functions:

             | f   g  |
W(f, g) = det|        | = f*g' - g*f'.
             | f'  g' |

EXAMPLES:

sage: wronskian(e^x, x^2)
-x^2*e^x + 2*x*e^x

sage: x,y = var('x, y')
sage: wronskian(x*y, log(x), x)
-y*log(x) + y

If your functions are in a list, you can use \(*' to turn them into arguments to :func:\):

sage: wronskian(*[x^k for k in range(1, 5)])
12*x^4

If you want to use ‘x’ as one of the functions in the Wronskian, you can’t put it last or it will be interpreted as the variable with respect to which we differentiate. There are several ways to get around this.

Two-by-two Wronskian of sin(x) and e^x:

sage: wronskian(sin(x), e^x, x)
-cos(x)*e^x + e^x*sin(x)

Or don’t put x last:

sage: wronskian(x, sin(x), e^x)
(cos(x)*e^x + e^x*sin(x))*x - 2*e^x*sin(x)

Example where one of the functions is constant:

sage: wronskian(1, e^(-x), e^(2*x))
-6*e^x

REFERENCES:

AUTHORS:

  • Dan Drake (2008-03-12)