Programing question

[Anonymous]

What is the best bit of code to use to avoid "divide by zero" errors?
I run into this issue often when using circular functions
such as in the following piece of code.

ratio=b/a
ang=atn(ratio)

If "a" happens to be zero there is an error.
Usually I resort to placing the following at the
beginning of the script.

if a=0 then a=0.0000001

This "work-around" is logically very dissatisfying to me.
Is there a better way?

Thank you,
Peter Devlin

[TomWaltz]

IF A <> 0 THEN
     ratio=b/a
     ang=atn(ratio)
ELSE
   (something to fix the problem)
ENDIF

[Anonymous]

Tom,
Thank you for your reply.
Its the "(something to fix the problem)"
that I was looking for.
Something more elegant than if a=0 then a=0.00000001.
Peter

[TomWaltz]

Where are A and B coming from?

[Anonymous]

Tom,
In the example I gave "a" and "b" are the obligatory
x and y dimensions of a library part.
But they could be any numeric parameter or variable
that has a possible value of zero either as initialized or
as the result of calculation.
Peter

[TomWaltz]

Peter

I was wondering if there was a certain situation this was coming from, that maybe there would be some kind of logic that would prevent it from happening. Since objects should probably never have an A or B value of 0, that should kickj up an error if its own.

[Anonymous]

Tom,
I appreciate your interest in this issue.
I made a library part that is a detail marker.
(see attached image)
I wanted (0,0) to be at the center of the "bubble"
and the point (a,b) to be at the edge of the call-out symbol
so that the connecting line between bubble and symbol
can be stretched to any angle and length and
still point to the center of the bubble similar to
what Red was trying to do in the thread titled "tangent".
The code must allow the library part's "A" to equal zero
to display the shape labeled #2
I know that there are ways to code this part so that
"A" equaling zero does not cause a problem, but
this is not the point I only use this lib part as an
example of where one value divides another value
and the dividing value may equal zero
and therefor cause an error.
Thanks,
Peter

[rocorona]

I don't have a more efficient solution. Usually, when I know that a divisor can became zero, I use the following form:

epsilon = 0.000001 ! <--at the beginning of the current (or Master) Script

ratio=b/MAX(a, epsilon)
ang=atn(ratio)

This way the error message can be avoided.
But, if the number can also be negative, the formula has to be more complex. ... I think something like this:

ratio=b / (MAX(ABS(a), epsilon) * (sgn(a)+(a=0)))

GASP!
_______________________________


--Roberto Corona--

[Laszlo Nagy]

rocorona wrote:
I don't have a more efficient solution. Usually, when I know that a divisor can became zero, I use the following form:

epsilon = 0.000001 ! <--at the beginning of the current (or Master) Script

ratio=b/MAX(a, epsilon)
ang=atn(ratio)

This way the error message can be avoided.
But, if the number can also be negative, the formula has to be more complex. ... I think something like this:

ratio=b / (MAX(ABS(a), epsilon) * (sgn(a)+(a=0)))

GASP!
_______________________________


--Roberto Corona--

Yes, this is similar to what GS programmers do in their GDL Scripts.
One can check out any AC9 Door or Window script and will find many examples similar to this:

IF ABS(Whatever) > EPS THEN
...............
ENDIF

EPS is for Epsilon.

[Anonymous]

I have always preferred a 'logical check';

oEpsilon = 0.0000001
ratio = oA / ( (oB=0) * Epsilon + oB )

For angles this is extended to;

oAngle = atn ( oA / ( (oB=0) * Epsilon + oB)

Oh how I wish we had 'proper' macro statements ...

oAngle = myATN (oA, oB)
!------
define macro "myATN" (value1, value2)
return atn ( value1 / ( (value2=0) * 0.000001 + value2)

- Stuart