Test model 958: error in experimental data

[luciansmith]

The parameter P21 (arccot(-0.1)) must be 1,670 and not -1,47.

Reported by: *anonymous

[luciansmith]

It took me a while to track down an independent source to confirm or deny this, but I finally found:

http://www.1728.org/trigcalc.htm

which confirms that the arccotangent of -0.1 is -1.4711 radians (or -84.289 degrees).

However, I also found graphs, such as the one at

http://en.wikipedia.org/wiki/File:Arctangent\_Arccotangent.svg

(from http://en.wikipedia.org/wiki/Arccotangent )

that seem to indicate that the arccotangent of everything is positive. Also, if you use one of the identities on the page:

arccot(x) = pi/2 - arctan(x)

and calculate that out, you also get 1.670.

So, in conclusion... what?

Original comment by: luciansmith

[luciansmith]

OK! I found the answer!

http://sbml.org/Forums/index.php?t=msg&th=504&rid=0

"The MathML standard states that the definitive answer is to be found in Abaramowitz and Stegun, section 4.4, where I find definitions which agree with mathword.wolfram.com and not with the CRC tables."

In other words, arccot should range:

-pi/2 < Acot(x) <= 0 (for x<-1)

This is confirmed in the mathml spec:

http://www.w3.org/TR/MathML2/appendixc.html\#cedef.arccot

Original comment by: luciansmith

[luciansmith]

• status: open --> closed

Original comment by: luciansmith