If x is a real constant, signum uses evalr to try to evaluate x to a floating-point number. See the Examples section.įor mathematical consistency, the value of signum(0), as determined either by the value of _Envsignum0 or by the third argument to signum, should be either not defined or a complex number of absolute value 0 or 1. If _Envsignum0 has a value, then only transformations which are valid everywhere, taking into consideration this assigned value of signum(0), can be applied. For example, if _Envsignum0 is not assigned a value, then any transformations which are valid everywhere except possibly at 0 can be applied. The value of _Envsignum0 determines which transformations and simplifications can be applied. In the 3-argument form, the third argument is not relevant and is ignored if the first argument is not 0. In this latter case, _Envsignum0 is set to the value of the third argument to signum while the signum call is evaluating, and is reset to its prior value upon exit from signum (see environment for further details). The value of the _Envsignum0 environment variable can be set globally by direct assignment, or for the duration of a single invocation of signum by using the 3-argument calling sequence. If _Envsignum0 is assigned a value, then signum(0) returns that value. For example, if _Envsignum0 is not assigned, then signum(abs(x)) simplifies to 1, while signum(-abs(x)) simplifies to -1. If _Envsignum0 is not assigned a value, then signum(0) is not defined, in that it can evaluate to anything.
The value of signum(0) is controlled by the environment variable _Envsignum0. It is defined by signum(x) = x/abs(x), for x ≠ 0. The signum command ( signum ) returns the "sign" of a real or complex number.
Sign function for real and complex expressions
0 kommentar(er)
