Value not multiplying by -1

Jay
2015 4 7
3 个回答
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更新时间：2015 4 7
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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)
end
end
end
i=i+1
end

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Adam
Adam 2015-4-7
Where does 'val' come from?
Jay
Jay 2015-4-7
Val is specified in previous code used prior.
I have not added it in yet as I was using it with prior code.
I use val to = 1 for this subroutine.
Adam
Adam 2015-4-7
So since you used breakpoints in the code where exactly is the problem? Is it not going into the relevant else-if statement or is the code in there not executing correctly?
Jay
Jay 2015-4-7
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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 采纳的回答

Thorsten
Thorsten 2015-4-7
编辑：Thorsten 2015-4-7

0 个投票

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.')
end
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).

更多回答（2 个）

Ingrid
Ingrid 2015-4-7

1 个投票

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

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Jay
Jay 2015-4-7
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 2015-4-7
编辑：Ilham Hardy 2015-4-7

1 个投票

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Jay
Jay 2015-4-7
I use break points to run through the code.
This is how I know where the problem originates from.
Ilham Hardy
Ilham Hardy 2015-4-7
Ok, did you also notice the mlint warning on your code?
e.g.:
There should not be empty char (read: space) between else and if. So, elseif instead of else if .
Jay
Jay 2015-4-7
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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