Getting the wrong math results, but why?

[hopbin9]

Hi guys, this is causing me some problems. Houdini is calculating this math incorrectly, and I don't understand why.

In the hscript textport I get the following

echo `2*cos($PI/6)`

1.99992

but if I do the same thing on a regular calculator, then I get the correct value

2*cos(PI/6) == 1.73

Why on earth is Houdini calculating this wrong? and can anyone else reproduce this problem?

[hopbin9]

I think cos($PI) should be -1, but in Houdini it's giving me 0.998497

I'm confused.

[hopbin9]

I was using this calculator.

http://www.mathopenref.com/calculator.html

Appears that it gives different results then the calculator with Windows. It's showing the same results for Houdini.

What I'm trying to do is calculate the apothem (inradius) of a n-sided polygon.

[hopbin9]

ah, i got it.

2 * cos(deg($PI/6))

Had to convert from radian first.

[Adam Ferestad]

Are the trig functions in Houdini calculated as Radian or Degree? I have always just assumed they are radians, though I have not used them all that much either. That will be some major knowledge for me eventually as I try to apply some of my math concepts to various parts of the program.

[old school]

Hscript expressions are degrees.

VEX/VOPs are in radians.

See example file of an identical sine wave in SOPs vs VOPs.

The not often used custom expressions are in radians.

trig_deg_vs_rad_expr_vs_vex.hip

Edited July 26, 2011 by old school