Making polynomial in matlab causes infinite loop

I am trying to make a polynomial function for several different coefficients. The problem is, something is wrong with my loop and matlab says

Maximum recursion limit of 500 reached. Use set(0,'RecursionLimit',N) to change the limit. Be aware that exceeding your available stack space can crash MATLAB and/or your computer.

I think the loop might be running infinitely, but I'm not sure how to fix this. I know matlab has a similar example for makeParabola, but I tried out their code and I get the same error.

function p = makePolynomial(a,b,c,d)

p = @polynomial

      function y = polynomial(x)
      y = a*x.^3 + b*x.^2 + c*x + d;
      end

firstp = makePolynomial(0,1,0,0);

secondp = makePolynomial(1,-3,0,1);

thirdp = makePolynomial(0,0,1,-1);

range = [-4,4];

figure;

hold on

fplot(firstp, range);

fplot(secondp, range, 'r:');

fplot(thirdp, range, 'ko');

hold off

end

Answer 1

[Image Analyst]

You have makePolynomial() calling itself, makePolynomial(). Why do you have this?

And why do you even have the unnecessary function polynomial()? It's not needed. What you do need is to make up a range for x. How does your code know if x has a thousand points from 3000 to 3489, or 150 points in the range 37 to 194, or whatever? It knows if you tell it, which you have not done. So assign some x - you might use linspace() for that -- then simply have this:

function p = makePolynomial(a,b,c,d)
  % Get x somehow......
  p = a*x.^3 + b*x.^2 + c*x + d;
  figure
  plot(x, p, 'b*-', 'LineWidth' 2, 'MarkerSize', 8);
  grid on;

If you want, you can have a test script to call this function with different a,b,c,d values:

makePolynomial(0,1,0,0); % Plotting is done inside
makePolynomial(1,-3,0,1);
makePolynomial(0,0,1,-1);

But of course, don't put that inside the makePolynomial() function itself!!!

You can either have the plotting done inside the function, like I did, or you can return the output and "x" into your test script, and plot it in the test script rather than the makePolynomial() function -- it's your choice.

[MG]

The problem is, I am supposed to make a nested function. I am supposed to follow what it says in here:

http://www.mathworks.com/help/matlab/matlab_prog/nested-functions.html

Under "Using Handles to Store Function Parameters", is the makeParabola. I am supposed to design something almost the same except I have makePolynomial. I can't use anything different.

[Image Analyst]

The problem is that your parent function is calling itself. I don't think you want to do that. You need another script that will call makePolynomial() several times. If you want, you can still have the other function in it nested, though you're still going to have to define x. What is the range of x, and which function, makePolynomial or the test program, do you want to define x in? Since x is not in the argument list of makePolynomial(), it seems like you need to define it inside of there. How are you going to define x???

[MG]

Yeah, you are right, somehow I forgot to do that. I meant to make "range" as x. I am still not getting the right thing, but at least I don't have the previous error anymore.

I also did as you recommended- I implemented everything after the nested function inside the command window instead, and erased it from the edit window, and I got the plot to work. There is no way, however, that I can implement these commands in the editor? I absolutely have to have them in command window, right?

[Image Analyst]

You should have two m-files. One function file called makePolynomial.m, and another to call that serrveral times with different values of a,b,c,d called testMakePolynomial.m, though you can call it one at a time from the command window if you want.