What does the dot mean? I have this formula: (k < 0.)

Greeintgs,

I am trying to understand an algorithm made by someone else. In an S-Function at some line I have the following:

double k = 0;

....

k = input2[0] - input3[0];

....

else if ((input1[0] < parameter1[0]) && (k < 0.))

Every input and parameter in my S-Function is a 1 row element ( vector with 1 element ).

I know that putting a dot means that you manipulate the elements of a vector individually. The things that confuses me is: k isn't a vector with multiple elements.

If k isn't a vector with multiple elements. Is there any purpose of the element wise comparison?

Answer 1

[Walter Roberson]

The code you are showing is C or C++ code, not matlab code. Any meaning matlab might give for dots is irrelevant; you have to look at what C or C++ do with the dots.

Anyhow it is simple. You are dealing with double precision numbers and 0. is the same thing as 0.0 which is a floating point zero.

In theory in C or C++ if k is double precision then

k < 0

with no dot means that you want to compare double precision k to (int) zero. Literal numeric constants in C and C++ default to integer if there is no decimal point in the literal.

So k<0 would in theory involve first loading an integer zero and then "widening" it to double precision zero before doing the comparison. Whereas since the source code does have the dot, k<0. involves loading a double precision zero directly and comparing that.

[Darius Vesa]

Makes so much sense. Thanks a lot!!