Skip a single statement depending on a boolean value

I have a statement which is an error depending on some boolean value. Is there a way to make the computer skip the one statement when that boolean is true / false?

Looking for a way to do it in one line and without while or if. Something that reminds this

x = x + (a<=b)*scalar_function(a,b)

[Sugar Daddy]

just put the boolean in the function (scalar_function) and apply if else there.

that's easy, everything will be on single line that way

[Jan]

@Sugar Daddy: Please calm down. The members of the forum are coming from different cultures and many do not speak English natively.

[yosef]

I'm curious what he said there before he edited it.

However, the "scalar_function" is not actually a function but another statement. You actually didn't help me that much

[Jan]

@yosef: The name "scalar_function" implies, that this is a function, which replies a scalar. I do not know, what "another statement" should be. Sugar Daddy's suggestion looks efficient. If it does not match your problem, explain the original procedure with more details.

[Jan]

@Sugar Daddy: Stop this.

Answer 1

[Walter Roberson]

piecewise is the only way to selectively execute expressions.

logical times expression still executes the expression. If execution of the expression would generate an error in the situation, you would get the error. If the expression generates infinity under the circumstances then you get 0 times infinite which would be nan. If the expression generates nan under the circumstances you would have 0 times nan.

[Walter Roberson]

%alternative
x = x + scalar_question_colon(a<=b, @()scalar_function(a,b), @()0);

function result = scalar_question_colon(condition, true_handle, false_handle)
  if all(condition)
      result = true_handle();
  else
      result = false_handle();
  end
end

You can see from the function name I gave that this is only designed to work with scalar operands. This is consistent with your code

x = x + (a<=b)*scalar_function(a,b)

as the * operation is matrix multiplication, also known as "inner product", which requires that at least one side be a scalar or else that the number of columns on the left is the same as the number of rows on the right. If a<=b were a vector then the * operator would fail if scalar_function given vector inputs did not return a scalar.

You can generalize to a non-scalar question_colon operator, but those cases get messier to code, as the context is often that you want to apply the two possibilities to the inputs selectively.

[yosef]

I'm much smarter now. Thank you