RAPID: compare decimal numbers

Alyssa Wells

VAR num var1 := 1.5708;

VAR num var2 := 1.5708;

IF var1 = var2 THEN

    TPWrite "Equal!"

ELSE TPWrite "Not equal!"

ENDIF

This code yields "Not equal!"

How can I compare these two values to get a result of equal?

Alyssa Wells2013-02-25 19:00:49

j_proulx

Hello Alyssa,

The following code works as expected and gives "Equal!" when run in Robot Studio.

 

MODULE MainModule
  VAR num var1 := 1.5708;
  VAR num var2 := 1.5708;

Proc main()
IF var1 = var2 THEN
    TPWrite "Equal!";
ELSE
    TPWrite "Not equal!";
ENDIF
ENDPROC

ENDMODULE

 

Henrik Berlin

Note that it is not recommended to compare floating point values with just a single "equal sign". It works for integers, but not for floats. Instead, you should judge two floats two be equal if they differ less than a very small constant value, epsilon, say. The value of epsilon should be defined with respect to the numerical accuracy of the data type, and the application. This is standard in numerical calculation and applies to all comparisons of floats done by computers, see the code example below.

[CODE]MODULE MyModule
  
  VAR num var1 := 1.5708;
  VAR num var2 := 1.5708;
  CONST num EPS := 0.0001;

Proc main()
IF Abs(var1 - var2) < EPS THEN
    TPWrite "Equal!";
ELSE
    TPWrite "Not equal!";
ENDIF
ENDPROC

ENDMODULE[/CODE]


If you are even more concerned with your numerical analysis you might want to take a look here.

You might also want to use the dnum data type (double precision instead of single). There are new methods to operate on it. For example AbsDnum, instead of Abs. See the RAPID Reference manual included in RobotStudio for details.



Henrik Berlin2013-02-26 15:02:39

j_proulx

Another solution may be to use the Truncate function.

MODULE MainModule
  VAR num var1 := 1.57087;
  VAR num var2 := 1.57082;
  VAR num var3 := 0;
  VAR num var4 := 0;
 
  PROC main()
      EqualTest;
  ENDPROC     

Proc EqualTest()
var3:=Trunc(var1Dec:=4);
var4:=Trunc(var2Dec:=4);
IF var3 = var4 THEN
    TPWrite "Equal!";
ELSE
    TPWrite "Not equal!";
ENDIF
ENDPROC

ENDMODULE

j_proulx2013-02-27 18:10:54