If statement using vectors

Hello,

I am trying to make an if statement that will check the values of vector "T_m", element by element, with vector "T_s". All variables are vectors of the same length 10080x1. The result should be a vector as well. The values that "P_actual" attain are always equal to "P", even though there are times that T_m is higher than T_s.

Here is the code:

if T_m > T_s

P_actual = P - 0.3*(T_m - T_s);

else

P_actual = P;

end

I would appreciate any sort of help or tips!

Answer 1

[Stephen23]

You cannot use if like that to operate element-wise on arrays (read the if help to know what your code is actually doing). You could use a loop, but that would be pointlessly complex for this simple task.

Method one: indexing:

P_actual = P - 0.3*(T_m-T_s);
idx = T_m>T_s;
P_actual(~idx) = P(~idx)

Method two: max:

P_actual = P - 0.3*max(0,T_m-T_s)

I recommend using the max method.

[Alexandros Katsikogiannis]

Thank you so much Stephen! The max function made things quite easy. However, there are still times at which I need to compare values between arrays.

For example:

if A > 0

will be true when each element of A is above 0. Similarly if I set A > B (both are vectors), then the statement would be true only if all elements of A are bigger than B. How can modify this to get a true or false statement for each element respectively?

Forgive me for the vagueness, but my fundamentals are quite weak.

[Alexandros Katsikogiannis]

Nevermind, I managed to do it with a combination of "for" and "if" loop statements. Thanks again!

[Stephen23]

Rather than using a loop, use logical indexing, as I showed in my answer.

Answer 2

[KALYAN ACHARJYA]

Your code doing the same

T_m=randi(6,1);
T_s=rand(6,1);
P=rand(6,1);
if T_m > T_s
P_actual = P - 0.3*(T_m - T_s);
else
P_actual = P;
end

Example 1: Here T_m>T_s

T_m =
     1     2     3     4     5     6
T_s =
    0.7224
    0.1499
    0.6596
    0.5186
    0.9730
    0.6490
P =
    0.8003
    0.4538
    0.4324
    0.8253
    0.0835
    0.1332
P_actual =
    0.7171    0.4171    0.1171   -0.1829   -0.4829   -0.7829
    0.1988   -0.1012   -0.4012   -0.7012   -1.0012   -1.3012
    0.3303    0.0303   -0.2697   -0.5697   -0.8697   -1.1697
    0.6809    0.3809    0.0809   -0.2191   -0.5191   -0.8191
    0.0754   -0.2246   -0.5246   -0.8246   -1.1246   -1.4246
    0.0279   -0.2721   -0.5721   -0.8721   -1.1721   -1.4721

Example 2: Here T_m<=T_s (Else Condition P_actual = P)

T_m =

    0.1734
    0.3909
    0.8314
    0.8034
    0.0605
    0.3993
T_s =
     1     2     3     4     5     6
P =
    0.5269
    0.4168
    0.6569
    0.6280
    0.2920
    0.4317
P_actual =
    0.5269
    0.4168
    0.6569
    0.6280
    0.2920
    0.4317