Re: Some trig trouble -- and IEEE floating point format

["Jonathon M. Merz" <merz@mscs.mu.edu>]

I too agree that the code looks good, but another (slight) possibility 
occurs to me:  Check the valid ranges for the Trig functions in the math 
package you are using.  While most packages do allow basically any value as 
the input to sin(), some do place restrictions, like requiring positive 
angles (id -0.5 PI radians must be converted 1.5 PI radians) or else the 
input might be restricted to the domain [0,2*PI) (ie, from 0 inclusive to 
2*PI NON-inclusive, so that 2*PI must be given as 0) - basically, just do a 
angle_rad % 2*PI to perform the conversion there.  Although in your code, 
angle_rad >= 2*PI will only occur if angle_deg >= 360.

Otherwise, I'd throw in some more printf's to find the exact values for 
angle_deg and angle_rad at every step to see if something you thought would 
be right turns out to be wrong.  I hope one of these shots in the dark 
might be helpful to you.

-Jon Merz

At 05:37 PM 9/5/00 -0400, you wrote:
>In a message dated 9/5/00 2:02:53 PM Central Daylight Time,
>lionelp@worldonline.co.za writes:
>
><<  double angle_rad, sine;
>
>     angle_rad = angle_deg * M_PI / 180.0;
>     sine = sin(angle_rad);
>
>     printf("The sine of %.2f is %.8f.\r\n", angle_deg, sine);
>
>  If I try to run this code, I get "Floating point error: Domain.",  >>
>
>Hmmm, nothing jumps out at me, but are you sure angle_deg is a valid number?
>Basically, if you plot the sine graph (x = value, y=sin(value)) the x values
>are considered "domain" and the y values are considered "range." So, the
>numbers you feed the sin() function make up the domain, and the results you
>receive make up the range. Therefore, this error means something is wrong
>with angle_deg. Is angle_deg a double as well? How about M_PI? Usually when I
>get a Domain error, I set up the formula wrong (180/(pi*degree)) instead of
>(pi*degree)/180. But that isn't what's wrong. Check to make sure angle_deg
>isn't an integer. If it is, this should work:
>
>     angle_rad = (double)angle_deg * M_PI / 180.0;
>
>Or I could be missing the error entirely.
>-Ender Wiggin
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