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odd trig function behavior

asked 2012-10-08 07:35:55 -0600

calc314 gravatar image

I get different behavior for trig functions at poles depending on how I evaluate them. For example:

f(x)=tan(x)^2-tan(x)
f(pi/2)

gives 0, which is disturbing.

Yet

f(x)=tan(x)*(tan(x)-1)
f(pi/2)

gives Infinity.

And,

tan(pi/2)^2-tan(pi/2)

gives

Infinity.

What's going on here?

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2 answers

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answered 2012-10-08 08:10:54 -0600

This is a bug in Pynac. I opened a ticket on trac (#13587).

Thanks for the report.

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answered 2012-10-08 11:39:25 -0600

achrzesz gravatar image

Maxima behaves better:

sage: maxima('f(x):=tan(x)^2-tan(x)')
sage: maxima('f(%pi/2)')
....
....
....
Maxima ERROR:

tan: %pi/2 isn't in the domain of tan.

# the same error messages in:
sage: maxima('f(x):=tan(x)*(tan(x)-1)')
sage: maxima('f(%pi/2)')          
sage: maxima('tan(%pi/2)^2-tan(%pi/2)')
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Comments

I agree. I prefer that behavior rather than returning infinity.

calc314 gravatar imagecalc314 ( 2012-10-08 12:59:41 -0600 )edit

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Asked: 2012-10-08 07:35:55 -0600

Seen: 163 times

Last updated: Oct 08 '12