plot() and fplot() give different results for the same function

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I'm trying to plot the function
between 0 and 100 (not including zero of course), but am running into a problem. When I use
x = linspace(0, 100, 10000);
y = 2.*sqrt(1+x)+((sin(sqrt(x).*pi).*sin(sqrt(1+x).*pi).*(2.*x+1))/(sqrt(x))) - 2.*sqrt(1+x).*cos(sqrt(x).*pi).*cos(sqrt(1+x).*pi);
I don't get the result I expected, which is the graph occasionally intersecting y = 0. However, by doing
fplot(@(x) 2.*sqrt(1+x)+((sin(sqrt(x).*pi).*sin(sqrt(1+x).*pi).*(2.*x+1))/(sqrt(x))) - 2.*sqrt(1+x).*cos(sqrt(x).*pi).*cos(sqrt(1+x).*pi), [0 100]);
I do get the result I expected.
I can't just use fplot, as I do need to use the variable y for other things, so I'm not sure what to do or what is even happening here. Any help would be greatly appreciated.

Accepted Answer

Bruno Luong
Bruno Luong on 15 Feb 2024
Edited: Bruno Luong on 15 Feb 2024
Your coding is wrong: Replace "/" with "./"

More Answers (1)

Torsten on 15 Feb 2024
Edited: Torsten on 15 Feb 2024
x = linspace(0, 100, 10000);
y = 2*sqrt(1+x)+sin(sqrt(pi)*x).*sin(sqrt(1+x)*pi).*(2*x+1)./sqrt(x) - 2*sqrt(1+x).*cos(sqrt(x)*pi).*cos(sqrt(1+x)*pi);
hold on
f = @(x)2*sqrt(1+x)+sin(sqrt(pi)*x).*sin(sqrt(1+x)*pi).*(2*x+1)./sqrt(x) - 2*sqrt(1+x).*cos(sqrt(x)*pi).*cos(sqrt(1+x)*pi);
fplot(f,[0 100])
  1 Comment
Bruno Luong
Bruno Luong on 15 Feb 2024
Edited: Bruno Luong on 15 Feb 2024
I believe fplot ezplot replace "*" "/" "^" etc... with elementwise operators ".*" "./', ".^". It interprets as standard math notation.
This how charming or quirking MATLAB is, depending on your taste.

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