How to find numerical roots for multivariable functions

Hi, I want to draw some graphs for my work. This is my function:

 function H_star=RHS1(H,h,theta,A);
  a=A.*((1.-H)./H).^(1-theta);
     if (1/a)*(1-1/a)>h;
        H_RHS=1/(2*a)-h^2*a^3/(2*(a-1)^2);
     else 
        H_RHS=0;
     end
   H_star=H_RHS-H;
end

I want to find a root for this function (as function of H). I tried to do it by this command (I set examples values for the parameters):

 fzero (inline('RHS1(H,0.1,0.6,1.1)'),0.5)

By this way I succeed to get an answer.

My question is how I can draw this fixed point as function of one of the parameters. For example, I want to plot the fixed point as function of A. I tried to do it in this way:

   j=1;
    for A=0.5:0.01:2;
     H_star(j)=fzero (inline('RHS1(H,0.1,0.6,A)'),0.5)
    j=j+1;
   end

But I get the message "Not enough inputs to inline function."

In adition, I want to get numeric derivatives of this fixed point according to the parameters.

Thanks!

Answer 1

[Star Strider]

I suggest this as a possible solution:

• Define h and theta in your workspace,
• Define A = 0.5:0.01:2; in your workspace,
• Create a for (or while) loop for j,
• Replace ‘for A=...’ with for k = 1:length(A)
• Create the anonymous function (instead of using the inline function) in the loop after the for k = 1:length(A) statement and then call fzero with it:

f = @(H) @RHS1(H,h,theta,A(k));
H_star(i,k) = fzero(f, 0.5);

This should get you started.

NOTE: I did not run your code, so my suggestions are untested but should work. Also, it is best not to use i and j as index counters, because MATLAB uses them for its imaginary operators.

[muly san]

Thank you very much! I will try it..

[Star Strider]

My pleasure!