what does the "-1" means in conditional statement?

Hi I am trying to understand a code which has some "if" statemets.

Now normally we pass true or false to the if else statement right? but in this case the state has a -1 what does this -1 means?

here is the line of code that I am trying to understand

 for i=1:CT.MaxSatNum
        clear tempsat;
        if (SimGlobal.aSatData(i).sOrbitData.sEphData.PRN~=-1)

Answer 1

[DGM]

Entering the if structure isn't conditional on -1, it's conditional on whether SimGlobal.aSatData(i).sOrbitData.sEphData.PRN is not equal to -1. The output of that test is a logical value.

A = 2;
if (A ~= -1)
    disp('tested true')
end

tested true

A ~= -1 % this returns a logical scalar

ans = logical
   1

[Imtiaz nabi]

ok but why is -1 used here? can we use 0 or something else?

[Stephen23]

"ok but why is -1 used here? can we use 0 or something else?"

That depends entirely on what the values of SimGlobal.aSatData(i).sOrbitData.sEphData.PRN can be, and what those values mean. The documentation of the code you are looking at should tell you that.

[Imtiaz nabi]

So I shouldn't worry about any rocket science here... there are only two statements true or false 1 and 0 right?

[Stephen23]

"there are only two statements true or false 1 and 0 right?"

MATLAB's logical class only has two values: true and false:

https://www.mathworks.com/help/matlab/matlab_prog/fundamental-matlab-classes.html

They are respectively equivalent to and often displayed as 1 and 0.