Parse error: usage might be invalid MATLAB syntax

So, I'm to write a function called trapint.m that takes data sample locations and function samples at those locations as input and returns an approximation of the integral over the sample range based on the trapezoidal rule. This is the detail of the instruction

This is what I did:

function I=trapint(x,fx)

N= max(size(fx));

N= max(size(x));

If n==N;

If isvector(x)==isvector(fx)==1;

If Isnumeric(x) == isnumeric (fx)==1;

h=(fx(1)-fx(N))/N;

i=2; y=0;

while i<=n-1 %%for summation of middle no between a and b

y = y+(fx(i));

i=i+1;

end

I=h/2*(fx(1)+2*y+fx(N));

ans=double(ans);

end

else

sprintf('error = x and fx are not of same length')

end

else

sprintf ('error =x and fx are not vectors')

end

else

Sprintf ('error= either data contained other than numerical value')

end

I got parse errors and invalid characters in lines 27,31,33,35,39 and 41. Thanks in advance

[Walter Roberson]

If isvector(x)==isvector(fx)==1;

tries to invoke a function named If with a single argument, like

If('isvector(x)==isvector(fx)==1');

You probably do not have a function named If. You probably do not have a function named Sprintf either.

MATLAB is case sensitive.

Your code has several Zero-Width Space characters https://www.fileformat.info/info/unicode/char/200B/index.htm . You can't see them, of course...

Answer 1

[madhan ravi]

fx=1:10 %an example of the vectors
x=10:20
I  =   trapint(x,fx)
function I=trapint(x,fx)

N= max(size(fx));

N= max(size(x));

if nargin(trapint)<2
    error('inputs must be two ')

if size(fx)~=size(x)
    error('not same size')

if isvector(x)~=1 & isvector(fx)~=1
    error('not vectors')

h=(fx(1)-fx(N))/N;

i=2; y=0;

while i<=n-1 %%for summation of middle no between a and b

y = y+(fx(i));

i=i+1;

end

I=h/2*(fx(1)+2*y+fx(N));

I=double(I); % whats ans here???

end
end
end
end

[madhan ravi]

I leave the rest to you to debug