CODEWITHSUNDEEP
matlabplot
romanocph
romanocph

Reputation: 38

Plotting a function in another .m file

i started programming Matlab the last week and i`ve been trying to plot a function file with no success.

This is my function file (impuls.m). It basicaly should set y = 0 for 0<=x<5 and x>10. y = 5 for 5<=x<=10).

function y = impuls(x)

    if ((x>=0 && x<5) || x>10)
        y=0;
    else if (x>=5 && x<=10)
            y=5;
        end
    end

end

I guess i did it right, because when i test it on my main file (fourierreihe.m) using impuls(1) i get a "0" and when using impuls(7) i get a 5. The problem is when i try to get all resuts for the interval [0 13] and plot them as a rectangular impuls.

I tried using:

impuls([0 13])

But i keep getting the error:

fouhierreihen
Operands to the || and && operators must be convertible to logical scalar values.

Error in impuls (line 3)
    if ((x>=0 && x<5) || x>10)

Error in fouhierreihen (line 1)
impuls([0 13])

Shouldnt i be getting something as "ans = 0 0 0 0 0 5 5 5 5 5 5 0 0 0" this as an answer?

So guys, what am i doing wrong? I`ve searched for videos and posts and i cant find the mistake there. How could i possibly plot it for the interval?

Thank you in advance, Pedro.

Upvotes: 1

Views: 331

Answers (2)

sco1
sco1

Reputation: 12214

As the error message and documentation explain, inputs to the short-circuit logical operators must be scalars. It doesn't really make sense fundamentally trying to robustly short circuit with two arrays of truth values.

You can use logical indexing to accomplish the same task in a vectorized manner. For example:

function y = impuls(x)
y = zeros(size(x));  % Initialize the output array
y(x>=5 & x<=10) = 5; % Condition one

Which returns:

impuls(1) =

     0


impuls(7) =

     5


impuls([0 13]) =

     0     0


impuls(0:13) =

     0     0     0     0     0     5     5     5     5     5     5     0     0     0

That your original function works with fplot is a concession from MATLAB's developers. The function documentation repeatedly states that the function being plotted must accept vector inputs (though they don't actually enforce it, apparently):

The function must accept a vector input argument and return a vector output argument of the same size

Your function doesn't do this, because && and || are scalar operations. However, fplot will revert to calculating function outputs element-by-element (a loop) in the event that the array input fails, throwing the following warning:

Warning: Function fails on array inputs. Use element-wise operators to increase speed. 
> In matlab.graphics.function.FunctionLine>getFunction
  In matlab.graphics.function.FunctionLine/updateFunction
  In matlab.graphics.function.FunctionLine/set.Function_I
  In matlab.graphics.function.FunctionLine/set.Function
  In matlab.graphics.function.FunctionLine
  In fplot>singleFplot (line 223)
  In fplot>@(f)singleFplot(cax,{f},limits,extraOpts,args) (line 182)
  In fplot>vectorizeFplot (line 182)
  In fplot (line 153)
  In trialcode (line 1)

Upvotes: 1

Brethlosze
Brethlosze

Reputation: 1618

My Friend....

Try this:

function y = impulse(t)
if 0
    %% Example
    t=(0:100)';
    y=impulse(t)
    plot(t,y);
end
for i=1:length(t)
    if ((t(i)>=0 && t(i)<5) || t(i)>10)
        y(i,1)=0;
    else if (t(i)>=5 && t(i)<=10)
            y(i,1)=5;
        end
    end
end

Note:

  • the for loop is critical in these cases,
  • the function impulse could exist anywhere, but your local version prevail,
  • the y(i,1) retain your vector as columns,
  • run the section inside the void loop (if 0)
  • the time is normally used here as variable :)....

hyp.

Upvotes: 0

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