Undefined function 'abs' for input arguments of type 'function_handle'

function [root,rootHistory, iter,errorValue]=myNewton(fh,dfh,initialGuess, tol , maxIter )

numLoop = 0;
rootHistory = [];

x = initialGuess;

a = @(x)fh;

while abs(a) >= tol 

      x1 = initialGuess - fh/dfh;

      initialGuess = x1;

      numLoop = numLoop + 1;

      rootHistory = [rootHistory x1];

      if numLoop == maxIter

          break

      end

end

root = x1; 

iter = numLoop;

errorValue = abs(fh(root));

end

I don't know why it is giving me this error statement. There are also other syntax error in my code as well. Can someone help please? The instructions are in the PDF

[bdlawr]

when i take out the "abs" it gives me this ==>

Undefined operator '>=' for input arguments of type 'function_handle'.

perhaps there is something wrong with my function handle? Sorry new to matlab...

Answer 1

[Walter Roberson]

You need to change

a = @(x)fh;

to

a = fh(x);

You need to change

to

        x1 = initialGuess - fh(SOMEINPUT)/dfh(SOMEINPUT);

You will need to figure out what is appropriate for SOMEINPUT.

You will also need to change a somewhere in the loop.

[bdlawr]

wait fh is function that i define as x^3 + 2x^2 - 10x. i need to plug in initialGuess into fh to test whether the while loop condition is true. thats why i used an anonymous fcn or am i using it incorrectly. there should be an image of the instruction under 'latest activity'. thank you so much for helping me

[Walter Roberson]

No, fh is a handle to a function. It says so right in your instructions.

To invoke a function handle, you name the function handle, then ( then the list of parameters then ) -- just like the fh(x) that I showed.

[bdlawr]

it now says

"Index exceeds matrix dimensions.

Error in myNewton (line 5) a = fh(x);"

but the autograder does give me 4 extra points

[Walter Roberson]

Please post your current code.

[bdlawr]

function [root,rootHistory, iter,errorValue]=myNewton(fh,dfh,initialGuess, tol , maxIter )

numLoop = 0;

rootHistory = [];

x = initialGuess;

a = fh(x);

while a >= tol 

      x1 = initialGuess - fh(x)/dfh(x);

      initialGuess = x1;

      numLoop = numLoop + 1;

      rootHistory = [rootHistory x1];

      if numLoop == maxIter

          break
      end
  end

root = x1; 

iter = numLoop;

errorValue = abs(fh(root));

end

[Walter Roberson]

In the first position, are you passing in

x.^3 + 2*x.^2 - 10*x

or are you passing in

    @(x) x.^3 + 2*x.^2 - 10*x

?