Adding functions in a for loop

I am trying to add a function in a for loop but I keep getting an error (Undefined function 'plus' for input arguments of type 'function_handle'). I would like to keep summing y(x) and plot the final result. Below is my script. Thanks ahead of time!

syms x

y = @(x) 1

for c = 1:5;

y = y(x) + @(x) 3*c.*((0 <= x) & (x <= 5))

x = linspace(0.2, 4, 500);

end

plot(x,y(x)

[Aquatris]

One thing you can do is to define the second function (y2 = @(x) 3*c.*((0 <= x) & (x <= 5)) before that summation. I do not think Matlab allows defining functions in an algebraic equation.

Secondly, when you define

y = y(x);

you are basically overwriting the y(x) function and the next time you call y(x), it will give you an error.

There might be an easier way of doing this. If you actually type your question, someone might write the code for you.

Answer 1

[OCDER]

Error is caused by adding a function handle to a value returned by a function handle. They're different things.

Y = y(x) + @(x) x^2  for instance, is equivalent to saying 
    value return by y(x) + a function name. Matlab goes : huh? What is 3 + name = ???

You don't need syms either it seems. You can do the following:

x = linspace(0.2, 4, 500);
y = @(x) 1; %This just returns 1 regardless of x. Is this what you want?
for c = 1:5
    YH = @(x) y(x) + 3*c.*((0 <= x) & (x <= 5));
    plot(x,YH(x))
end

I'm confused as to what you're expecting to plot, other than a line. Recheck YH, the function handle.

[Jeff]

I was just using an easy example; which is why I chose to plot a line. I want a function y(x) to be calculated and added to its previous value on every iteration.

In other words, the output of this loop would be y(1) + y(2) + y(3) + y(4) + y(5). At least that is my intent. Hope that makes sense. Thanks for the input!

[OCDER]

I see. In that case, something like this might work.

x = linspace(0.2, 4, 500);
y = @(x) 1; %This just returns 1 regardless of x. Is this what you want?
for c = 1:5
    YH = @(x) y(x) + 3*c.*((0 <= x) & (x <= 5));
    if c == 1
        y_all = YH(x);
    else
        y_all = y_all + YH(x);
    end
end
plot(x,y_all)

[Stephen23]

"the output of this loop would be y(1) + y(2) + y(3) + y(4) + y(5)"

Adding function handles in a loop seems a pointlessly complex way to achieve that, especially as the function you are adding is always the same. Why not just:

• define one function before the loop, and call that inside the loop (or use arrayfun).
• write efficient vectorized code?

[OCDER]

Yeah, I agree with Stephen - making a ton of function handles is not the right way to go. Making a function that takes input x and c would be better. Example:

x = linspace(0.2, 4, 500);
y = @(x) 1; %This just returns 1 regardless of x. Is this what you want?
YH = @(x, c) y(x) + 3*c.*((0 <= x) & (x <= 5));
for c = 1:5
    if c == 1
        y_all = YH(x, c);
    else
        y_all = y_all + YH(x, c);
    end
end
plot(x,y_all)

[Jeff]

Thanks for the input! I was able to get my code to work.