MATLAB: Matlab function defining problem

function definingMATLAB

hi everybody!

I want to ask how to define a function in MATLAB. For example,part of the code is like that:

function program1(xl,xu,es,imax,xr,n,ea)
n=0;
f=input('Enter the function f:','s');
inline(f)
ezplot(f)
xl=input('Seeing the graph,decide on the first initial guess:');
xu=input('The upper initial guess:');
fl=f(xl);
fu=f(xu);
tol = input('Enter tol ');
ea = 1e8;
iu = 0; 
il = 0;
xr_old = 0;
n = 0;
while ea > tol
   n = n+1;
   xr = xu - fu*(xl-xu)/(fl-fu);
   fr = f(xr);
   ea=100*abs((xr-xr_old)/xr);
   if fu*fr < 0;
      xl= xr;
      fl = fr;
      il = 0;
      iu = iu+1;
.....................

I cannot define the function f of x, so , i guess the program takes my x s as index and gives me

Attempted to access f(0); index must be a positive integer or logical.
Error in program1 (line 10)
fl=f(xl);

So, how can I fix this?

Thank you in advance.

Best Answer

When you enter a function f you should enter for example for sine function

@sin

Related Solutions

MATLAB: Presenting this results in a tabulated form

Holy lack of semi-colons! Try this:

home
f=@(x)x^10-1;
xl=0;
xu=1.3;
xr = xu;
es=0.01;
fl=f(xl);
fu=f(xu);
iter=0;
iu = 0; 
il = 0;
fprintf('\n\n%10s%10s%10s%10s%10s%10s%10s%10s\n',...
        'iter','xl','xu','f(xl)','f(xu)','xr','f(xr)','ea')
fprintf(['      ',repmat('-',1,74),'\n'])    
while 1
    xrold = xr;
    xr = xu - fu*(xl-xu)/(fl-fu);
      fr = f(xr);
      iter=iter+1;
      if xr<0
      elseif xr>0
          ea=abs((xr-xrold)/xr)*100;
      end
      test = fl*fr;
      if test<0
          xu = xr;
          fu = f(xu);
          iu = 0;
          il = il+1;
          if il>=2
              fl=fl/2;
          end
      elseif test>0
          xl=xr;
          fl=f(xl);
          il=0;
          iu=iu+1;
          if iu>=2
              fu=fu/2;
          end
      else
          ea=0;
      end
      if ea<es
          break
      end
      fprintf('%10.2i%10.2f%10.2f%10.2f%10.2f%10.2f%10.2f%10.2f\n',...
              iter,xl,xu,f(xl),f(xu),xr,f(xr),ea)
end
fprintf('\n\n')
ModFalsePos=xr;

MATLAB: How to find positive x-root of this function

Okay, in this line here:

ea=abs((xr-xold)/xr)*100

ea is always going to be zero, since a few lines above, you assigned xold=xr. Thus your algorithm always exits after the first iteration. So you need to flip the first lines after while:

    xrold = xr;
    xr = xu - fu*(xl-xu)/(fl-fu);

Then, you need to initialize iu, il and xr outside of the loop.

xu=1.3;
xr=xu;
iu = 0; il = 0;

Also, remove the function line and the last end, what you have here is a script, not a function. If you want it to be a function, at least f should be an input argument, too, otherwise it doesn't make much sense.

And now it should be running.

Best Answer

Related Solutions

MATLAB: Presenting this results in a tabulated form

MATLAB: How to find positive x-root of this function

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