Adding functions in a for loop

Question

Jeff 2018-7-19

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评论： Jeff 2018-7-25

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)

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Aquatris 2018-7-19

在 MATLAB Online 中打开

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.

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Answer 1

OCDER 2018-7-19

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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.

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OCDER 2018-7-19

在 MATLAB Online 中打开

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 2018-7-25

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

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Adding functions in a for loop

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