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## Re: Problems with functions

**From**: |
Tatsuro MATSUOKA |

**Subject**: |
Re: Problems with functions |

**Date**: |
Wed, 20 Jul 2016 12:22:56 +0900 (JST) |

----- Original Message -----
>* From: mat_hunt *
>* To: help-octave> Cc: *
>* Date: 2016/7/20, Wed 05:37*
>* Subject: Problems with functions*
>* *
>* I have defined a function:*
>* *
>* function y=f(x)*
>* y_1=x(1)-x(2)+x(3)-2;*
>* y_2=2*x(1)-x(2)+x(3)-3;*
>* y_3=2*x(1)+x(2)-x(3)-1;*
>* y=[y_1 y_2 y_3];*
>* endfunction*
>* *
>* and I have written a function to compute the Jacobian of that function:*
>* *
>* function J=jacobian(func,x)*
>* % computes the Jacobian of a function*
>* n=length(x);*
>* fx=feval(func,x);*
>* eps=1.e-8; % could be made better*
>* xperturb=x;*
>* for i=1:n*
>* xperturb(i)=xperturb(i)+eps;*
>* J(:,i)=(feval(func,xperturb)-fx)/eps;*
>* xperturb(i)=x(i);*
>* endfor;*
>* endfunction*
>* *
>* when I use the command:*
>* *
>* jacobian(f,[1 1 1])*
>* *
>* I get the error:*
>* *
>* error: 'x' undefined near line 2 column 5*
>* error: called from:*
>* error: /home/mat/Matlab programs/f.m at line 2, column 4*
>* error: evaluating argument list element number 1*
>* *
>* What is going on? The code was working perfectly fine 10 minutes ago and now*
>* it's throwing up errors.*
>* *
This is not an answer but a comment.
You can calculate numerical jacobinan function "jacobs" in the optim package.
http://octave.sourceforge.net/optim/function/jacobs.html
Tatsuro