how to formulate if statement for a vector?

A=[-3,-2,-1,1,2,3]
B=[-3,-2,-1,2,3,4]

i have 4 condition and have to slect only one when it satisfies.

1. negative A negative B i.e. A=[-3,-2,-1,0,0,0] B=[-3,-2,-1,0,0,0]
2. negative A positive B .
3. positive A negative B.
4. positive A positive B.

How can i select only one condition if input is in vector.

[Stephen23]

Use logical indexing.

[Shubham Mohan Tatpalliwar]

yes i have used logical factors to create the 0 0 0 to convert the unwanted negative or positive values.

[Steven Lord]

The elements at some of the locations of your vectors satisfy your first condition. Others satisfy the fourth condition. Do you want to choose one of those conditions at random and apply it to the entire A and B vectors, or do you want to apply the condition that each pair of corresponding elements satisfies to that element of the result?

What do you want to do if none of the conditions are satisfied?

A = zeros(1, 6);

The elements of A are neither positive nor negative.

[Shubham Mohan Tatpalliwar]

 each pair of corresponding elements satisfies to that element of the result?

What do you want to do if none of the conditions are satisfied?

it would not happen.

also if the one condition does not satisfy the answer would be zero

Answer 1

[Torsten]

if A<=0 & B<=0
  ...
elseif A<=0 & B>=0
  ...
elseif A>=0 & B<=0
  ...
elseif A>=0 & B>=0
  ...
end

[Shubham Mohan Tatpalliwar]

does this work for vector inputs? because i have thousands of values

[Torsten]

Yes, A>=0 tests whether all elements of A are nonnegative, e.g.

[Shubham Mohan Tatpalliwar]

Operands to the and && operators must be convertible to logical scalar values.

it shows this error

[Torsten]

Why do you use "&&" ? I only used "&".

[Shubham Mohan Tatpalliwar]

matlab recommended it... will try it to do with only &

[Shubham Mohan Tatpalliwar]

if the condition does not satisfies the answer should be zero.... for example if 4 satisfies then 1 2 3 would be zzero....

how should i modify my program for this

[Torsten]

I must admit that I don't fully understand what you mean.

Maybe this

condition = zeros(4,1);
if A<=0 & B<=0
  condition(1) = 1;
elseif A<=0 & B>=0
  condition(2) = 1;
elseif A>=0 & B<=0
  condition(3) = 1;
elseif A>=0 & B>=0
  condition(4) = 1
end

?

Best wishes

Torsten.

[Jan]

If A and B are vectors, the expression

if A<=0 & B<=0

is converted internally to:

if all(A(:)<=0 & B(:)<=0) & ~isempty(A) & ~isempty(B)

Writing this explicitly is less confusing in my opinion. Array-valued conditions of if commands are a frequent source of bugs.

[Shubham Mohan Tatpalliwar]

Can i also use it for 3 variables?