Function, dot, help me for solution

% I couldnt find my mistake

v=19*10^-3;   
N=314;  
R=25*10^-3;   
L=50*10^-3;    
C=1*10^-4;    


e=0.1:0.1:0.9;
W=@(e) v*N*R*L*(L/C)^2*(e./4).*((16*e.^2+pi^2*(1-e.^2))^0.5/(1-e.^2).^2);
%W depends on e
sm=@(W) v*N*L*R/(4*W.*(L/C)^2);
%sm depends on W

plot(e,sm(W))

Operator '*' is not supported for operands of type 'function_handle'.

Error in solution (line 13)
sm=@(W) v*N*L*R/(4*W.*(L/C)^2);

[Adam Danz]

I ran your code to produce the error. In the future, you can run your code using the Run Feature (Green triangle button in the tool strip).

[Gloria]

I didnt understand how can I fix the problem

[Adam Danz]

The error message tells you the problem.

sm=@(W) v*N*L*R/(4*W.*(L/C)^2);

^ W is a function handle

Perhaps you meant to provide an input to W()?

[Gloria]

I guess I am making mistake with dot , the place of the dot is wrong,even this part of the code dose not working

v=19*10^-3;

N=314;

R=25*10^-3;

L=50*10^-3;

C=1*10^-4;

e=0.1:0.1:0.9;

W=@(e) v*N*R*L*(L/C)^2*(e./4).*((16*e.^2+pi^2*(1-e.^2))^0.5/(1-e.^2).^2);

figure

plot(e,W(e))

[Walter Roberson]

W = @(e) v*N*R*L*(L/C)^2*(e./4).*((16*e.^2+pi^2*(1-e.^2))^0.5./(1-e.^2).^2);

Answer 1

[Benjamin Kraus]

This line has the error:

sm=@(W) v*N*L*R/(4*W.*(L/C)^2);

Specifically: W is an anonymous function, so you can't do 4*W. That is what is generating the error message.

You need to evaluate your function W using some value of e before you can multiply it by 4. Alternatively, don't even create an anonymous function, and instead create W using the value of e from the previous line:

v = 19*10^-3;
N = 314;
R = 25*10^-3;
L = 50*10^-3;
C = 1*10^-4;
e = 0.1:0.1:0.9;
W = v.*N.*R.*L.*(L./C).^2.*(e./4).*((16.*e.^2+pi.^2.*(1-e.^2)).^0.5./(1-e.^2).^2);
sm = v.*N.*L.*R./(4.*W.*(L./C).^2);
plot(e,sm);

[Gloria]

Thank you so much!

I have another question. What if I also want to define 3 different L, I want to have three different line on the graph for L*1, L*2 and L*3.

How can I write function for this?

[Benjamin Kraus]

If you have three different values for L, you can either create three instance of W and three instances of sm (i.e. W1, W2, etc.), or you can define W and sm as anonymous functions that take L as an input parameter, as @John D'Errico suggested in their answer.

Alternatively, you can leverage implicit expansion by defining L as a column vector and e as a row vector (or vice versa), as described in this blog post, but that's a bit of an advanced manuever.

Answer 2

[John D'Errico]

Your problem has NOTHING to do with dots. This is a common mistake we see made here.

Suppose you have a pair of function handles, and you want to "add" the functions together? For example, suppose we try this:

F1 = @(x) x.^2;
F2 = @(x) x+1;

One might hope that the sum of those two function handles would be just a new function handle. I might try to write it as F3 = F1 + F2. If I did however, MATLAB would throw an error, just as you found. Instead, you need to create a new function handle, by adding the results of each of the two.

F3 = @(x) F1(x) + F2(x);

As you can see, we can use it as we would expect to happen.

F3(5)

ans = 31

Had I just tried to add or multiply the two function handles together, we would an error as you saw:

F1 * F2

Operator '*' is not supported for operands of type 'function_handle'.

As I said, you CANNOT add, multiply, subtract or divide function handles. Arithmetic operations do not apply to function handles. You need to do it as I showed above.

[Gloria]

Thank you so much!