I keep getting an error: Attempted to access x(2); index out of bounds because numel(x)=1. in my newtmult code. Please help!

This is my code:

function [J,f]=jfreact(x,y,varargin)
df1dx1=2*x;
df1dx2= -1;
df2dx1= -2*x;
df2dx2= -2*y;
J=[df1dx1 df1dx2;df2dx1 df2dx2];
f1=u(x(1),x(2));
f2=v(x(1),x(2));
f=[f1;f2];
function f=u(x,y)
f = x^2-y-1;
function f=v(x,y)
f = 5-y^2-x^2;

i am trying to use newtmult function to solve the system of linear equations with an initial guess of x=y=1.5. any help would be greatly appreciated.

[Walter Roberson]

Please show your code that invokes newtmult. Please also clearly show which line the error is occurring on.

newtmult() is not a Mathworks provided function. Are you using a routine out of Numerical Methods In MATLAB, such as is found at http://www.nd.edu/~msen/Teaching/NumMeth/Programs/BookMfiles/newtmult.m ?

Answer 1

[Matt J]

You cannot write jfreact as function of separate arguments x and y.

[J,f]=jfreact(x,y,varargin)

newtmult expects you to bundle all of the unknowns into a single vector and pass that vector as the first input argument:

function [J,f]=jfreact(xy,varargin)

    x=xy(1);
    y=xy(2);

df1dx1=2*x;
df1dx2= -1;
df2dx1= -2*x;
df2dx2= -2*y;
J=[df1dx1 df1dx2;df2dx1 df2dx2];
f1=u(x(1),x(2));
f2=v(x(1),x(2));
f=[f1;f2];