multiple if statements in matlab

2012 12 16
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% inputs are a_s, p, t, a
% a_s=single number
% p,t,a are (nX1) column vectors each
% output is P (also a column vector of dimension (nX1))
%---------actual equations--------
if a_s<a<=a_s-180
P=p+t for p<=180-t
P=p+t-180 for p>180-t
if a<=a_s or a_s-180<a
P=p-t for p>=t
P=p-t+180 for p<t
Note: The two if's are connected.
%---Matlab prog. for above eqn.---
if a_s<a<=a_s-180
if p<=180-t %------(1)
P=p+t;
elseif p>180-t %------(2)
P=p+t-180;
end
elseif a<=a_s | a_s-180<a
if p>=t %------(3)
P=p-t;
elseif p<t %------(4)
P=p-t+180;
end
end
% I couldn't figure the mistake. While running the program, (1)&(3) are
% ignored in matlab.

3 个评论
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Image Analyst
Image Analyst 2012-12-16
After you supply sample/typical values for a_x, p, t, and a, then I will run it. Off the top of my head it looks like this could be vectorized.
Rakesh
Rakesh 2012-12-16
Thanks for the reply. Here are few values of the variables:
a=[10 11 55 22 25 34 39 40 41 52 54 76 113 125 133];
p=[40 51 40 22 45 19 97 79 135 222 175 138 125 77 20]';
t=[80 75 45 71 71 63 61 72 89 78 73 54 9 54 65]';
a_s=283;
Jürgen
Jürgen 2012-12-16
编辑：Jürgen 2012-12-16
as said above the code works fine , but see my answer: I still wonder what you want to do, you gave us a column vectors a, p and t so with those inputs and the provided code you can only run the program and see that none of your conditions are fullfilled, unless if you want to run it elementwise then you need to add a for loop for indexing, but in that case you can calculate it directly with the vector, e.g. by using the result of comparing a to a_s (zero and ones) to multiply with -t and +t

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Jürgen
Jürgen 2012-12-16
编辑：Jürgen 2012-12-16

0 个投票

Hey, difficult to check it without example values but if I understand it well you are comparing a column vector p to a column t, so then all element needs to be larger or smaller than the ones in the other column no? or do you want to compare element wise

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Image Analyst
Image Analyst 2012-12-16

1 个投票

How can this ever be true:
a_s< a <= a_s-180
A number can't be greater than a certain number and also less than the number, and certainly not less that that number minus 180!

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Jürgen
Jürgen 2012-12-16
okay should have noticed that :-)
Matt Fig
Matt Fig 2012-12-16
编辑：Matt Fig 2012-12-16
In MATLAB this statement could easily be true. For example:
>> a_s = 200;
>> a = 1;
>> a_s< a <= a_s-180
ans =
1
Jürgen
Jürgen 2012-12-16
Hey Matt, could you explain that please? I normally use: a_s< a& a <= a_s-180 and that gives as expected ans = 0 so they other statement acts as an "or" operator or what? regards,J
Image Analyst
Image Analyst 2012-12-16
Yes that's correct. We see this all the time, and know that often causes problems because that is not what the user was intending when he coded it up. Jurgen you should use && in that situation, because it's a boolean test, not a bit-by-bit operation that you want to do.
Matt Fig
Matt Fig 2012-12-16
编辑：Matt Fig 2012-12-16
MATLAB evaluates left to right. So as you wrote it, the expression evaluates this way
(a_s< a) <= a_s-180
What you probably meant was
a_s< a && a<= a_s-180
But then IA's original comment applies.

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