How to use if statements with arrays?

I am trying to use an if statement with an array,

T = 300:300:1800
for i = 1:4
%condition 1
if T(i) <= 500
A =  28.98641;
B = 1.853978;
y = A*T+B*T^2/2
else 
%condition 2
 A =  19.50583;
 B = 19.88705;
y = A*T+B*T^2/2
end
end

I want the result to take y from "condition 1" if T is lower or equal to 500 and from "condition 2" if T is grater than 500.

However, the outcome always gets the result from condition 2.

[Stephen23]

"How to use if statements with arrays?"

Usually the best answer is "don't". Just use logical indexing, it is simpler.

[M Talha Rehman]

What is the role of this function here " i = 1:4" in the above program?

Answer 1

[madhan ravi]

Note: The below can be achieved using logical indexing which is easier and less work to do.

T = 300:300:1800
y=zeros(1,4); % prellocate   %% I suspect 4 should be numel(T)
for i = 1:4
%condition 1
if T(i) <= 500
A =  28.98641;
B = 1.853978;
y(i) = A*T(i)+B*T(i)^2/2;   % use iterator as index -> (i)
else 
%condition 2
 A =  19.50583;
 B = 19.88705;
y(i) = A*T(i)+B*T(i)^2/2;
end
end

[Bruna Araújo]

Thank you!!!!!!

[madhan ravi]

Anytime :)

[Bruna Araújo]

When I changed the variable T to

T = [298.15;293.15;408;600] ; 

The problem started again, the loop is only providing me results from condition 2.

I changed the T(i)<500 to T(i)<500.00 but it didn't make any difference.

[madhan ravi]

nah , it's giving the right values

Answer 2

[Jos (10584)]

You need to assign the i-th calculation the i-th element in y in the two conditions

y(i) = ...

To speed things up, especially for large loops, you can pre-allocate y before the loop

y = nan(1,4) % assuming the loop is 4