Solve MATLAB fsolve Equation: x-(r/4)*sin(pi*x)=0

[krnhseya]

I think I posted in a wrong forum...I wasn't sure which category I was supposed to post this under but here it goes...

1. Homework Statement

Find x where r varies from 0 to 4.

2. Homework Equations

x-(r/4)*sin(pi*x)=0

3. The Attempt at a Solution

The problem that I ran into with MATLAB is that when I create a sub-m file for fsolve, it requires 2 equations whereas I only have 1 equation.

function F=myfun(x,r)
F(1)=x-(r/4)*sin(pi*x);

My executable is:

var_new=[];
for r=0:0.01:4;
var=fsolve(@myfun,0.5)
var_new=[var_new var]
i=i+1;
end

I expect to get "var" variable to be a single number where my "relevant equation" is set to zero. var_new is simply creating an array for me to plot r versus var.

Thank you.

 

[krnhseya]

So 1 equation and 1 variable...Looks darn easy but I just can't figure this out and MATLAB examples that I can find (including built-in help) doesn't get me any more help...Anyone...?

 

[krnhseya]

My new attempt...

i=1;
new_x=[];
newnewx=[];

for r=0.5:0.01:4;
new_x(i)=fsolve(@myfun,[0 r]);
newnewx(i)=((r*pi)/4)*cos(pi*new_x(i));
i=i+1;
end
r=0.5:0.01:4;

plot(r,newnewx)

where the myfun is:

function F=myfun(x)
x=x(1);
r=x(2);
F(1)=x-((r/4)*sin(pi*x));

 

[bob1182006]

What you can do is define r outside of the loop, then loop through a variable i that goes from 1:length(r). Inside of the loop define the function F so that r is not a variable but a constant for each iteration.

But if you need to have the function in a separate script you can try and create a new function F2(x) = F(x,r) where r is some specific number. I don't think fsolve will just accept a multivariable function.