Using inverse trigo functions doesn't solve equations fully

Question

Using inverse trigo functions doesn't solve equations fully

Closed this issue 7 years ago · 3 comments

Example:

(solve 'x (ex (= 1 (atan x)))) => #{(tan 1)}
(solve 'x (ex (= 1 (asin x)))) => #{(sin 1)}

whereas

(solve 'x (ex (= 1 (sin x)))) => #{1.5707963267948966}
(solve 'x (ex (= 1 (tan x)))) => #{0.7853981633974483}

Answer 1 · 2017-04-06T13:48:03.000Z

Actually the problem happens with normal trigonometry functions as well:

(solve 'x (ex (= x (* (tan 1) 1))))  => #{(tan 1)}
(solve 'x (ex (= x (* (atan 1) 1)))) => #{0.7853981633974483}

Answer 2 · 2017-04-06T14:23:35.000Z

Seems like the numeric.expresso.properties/props multi method is missing definitions for sin/cos/tan. Adding the definitions fixes the problem.
I'll send a PR with the missing definitions.

Answer 3 · 2017-04-07T05:59:22.000Z

Thanks. The trigonometric functions should be standard and provided by the library.
Note that if you have other (nonstandard) functions that you want expresso to execute after simplification you can extend the props multimethod in your application code.