Value not multiplying by -1

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Jay on 7 Apr 2015
Edited: Thorsten on 7 Apr 2015
I have a nested if statement which works as it is supposed to until the last iteration.
Does anyone know why it is not multiplying the last value by -1?
w = x_0 % zero vector
k = 0 % zero value
i=1 % initial value for count
j=-1 % coefficient
for i = 1:n
if Raw_Data(i,2) == Raw_Data (i,3)
fprintf ('ERROR!!!!!)
else if Raw_Data(i,3) == val
w(i,1) = Raw_Data(i,4)
else if Raw_Data(i,2) == val
w(i,1) = j* Raw_Data(i,4)
% Rationalisation Not Working
else w(i,1)= j* Raw_Data(i,4)
Jay on 7 Apr 2015
The code is not executing correctly.
Namely the
elseif Raw_Data(i,2) == val
w(i,1)= j* Raw_Data(i,4)
The element is not multiplying by -1.
The value is already -ve so I want to multiply it by -1 again to = +ve value.

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Accepted Answer

Thorsten on 7 Apr 2015
Edited: Thorsten on 7 Apr 2015
I would suggest to avoid the loop and use logical indexing:
ind = Raw_data(i,3) == val;
w(ind) = Raw_data(:,4);
w(~ind) = j*Raw_data(:,4);
if any(Raw_Data(i,2) == Raw_Data (i,3))
error('values in column 2 and 3 are identical.')
Note that in your code
else if Raw_Data(i,2) == val
is not needed, because
w(i,1) = j* Raw_Data(i,4)
in any case.
And if w is a vector, w(i) is the same as w(1,i).

More Answers (2)

Ingrid on 7 Apr 2015
in a for loop there is no need to increment the i so just leave out
i = i+1
as this is done automatically.
Also do not use the i as this can be confusing when using imaginary numbers, better practice is to use ii or something completly else (for example counter )
It is not clear why there is an
else if Raw_Data(i,2) == val
when you perform the same function regardless of true/false of this expression
  1 Comment
Jay on 7 Apr 2015
I will leave out the incremental addition.
I will also change the variable from i to something more suitable.
I don't see how
else if Raw_Data(i,2) == val
is performed regardless, val is a dynamic variable.
else w(i,1)= j* Raw_Data(i,4)
was used to try and rectify the issue of the final element not multiplying by -1.

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Ilham Hardy
Ilham Hardy on 7 Apr 2015
Edited: Ilham Hardy on 7 Apr 2015
Jay on 7 Apr 2015
Ok, I will do that from now on.
It does not throw an error if I use else if. Is there a difference in the function elseif and else if?

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