How to solve a series of equations using a loop in MATLAB?

Question

I'm trying to solve the following series of equations and store the positive solution for each equation

Here's the code I've used:

s=zeros(1,100);

for i=1:100
   syms l0 positive
   eqn(i)= .0017777*(l0^.25)/(.05-l0) == i;
   s(i)=solve(eqn(i),l0);
end

But at the end I get the following error:

The following error occurred converting from sym to double: Unable to convert expression into double array.

Could anyone please help me to solve this problem?

Answer 1

Because of the 1/4 power in your equation, there are complex solutions.

You only want the real solutions, so specify that...

solve(eqn(i),l0,'Real',true);

This will give you the results you want.

Note that MATLAB automatically does the conversion from the symbolic output of solve to a double, because you initialised s to be an array of doubles, not a symbolic array. You lose precision here, but can use the answer as you would any other double array.