Add step function to GiNaCs built-in functions.

[ginac.git] / ginac / inifcns.cpp

diff --git a/ginac/inifcns.cpp b/ginac/inifcns.cpp
index 9a488fe9219b383ff2111a6bc0a808bf14d67a6e..830b1bff41ff556816e6c398add542179ad6f7e2 100644 (file)
--- a/ginac/inifcns.cpp
+++ b/ginac/inifcns.cpp
@@ -123,6 +123,82 @@ REGISTER_FUNCTION(abs, eval_func(abs_eval).
                        conjugate_func(abs_conjugate).
                        power_func(abs_power));
 
+//////////
+// Step function
+//////////
+
+static ex step_evalf(const ex & arg)
+{
+       if (is_exactly_a<numeric>(arg))
+               return step(ex_to<numeric>(arg));
+       
+       return step(arg).hold();
+}
+
+static ex step_eval(const ex & arg)
+{
+       if (is_exactly_a<numeric>(arg))
+               return step(ex_to<numeric>(arg));
+       
+       else if (is_exactly_a<mul>(arg) &&
+                is_exactly_a<numeric>(arg.op(arg.nops()-1))) {
+               numeric oc = ex_to<numeric>(arg.op(arg.nops()-1));
+               if (oc.is_real()) {
+                       if (oc > 0)
+                               // step(42*x) -> step(x)
+                               return step(arg/oc).hold();
+                       else
+                               // step(-42*x) -> step(-x)
+                               return step(-arg/oc).hold();
+               }
+               if (oc.real().is_zero()) {
+                       if (oc.imag() > 0)
+                               // step(42*I*x) -> step(I*x)
+                               return step(I*arg/oc).hold();
+                       else
+                               // step(-42*I*x) -> step(-I*x)
+                               return step(-I*arg/oc).hold();
+               }
+       }
+       
+       return step(arg).hold();
+}
+
+static ex step_series(const ex & arg,
+                      const relational & rel,
+                      int order,
+                      unsigned options)
+{
+       const ex arg_pt = arg.subs(rel, subs_options::no_pattern);
+       if (arg_pt.info(info_flags::numeric)
+           && ex_to<numeric>(arg_pt).real().is_zero()
+           && !(options & series_options::suppress_branchcut))
+               throw (std::domain_error("step_series(): on imaginary axis"));
+       
+       epvector seq;
+       seq.push_back(expair(step(arg_pt), _ex0));
+       return pseries(rel,seq);
+}
+
+static ex step_power(const ex & arg, const ex & exp)
+{
+       if (exp.info(info_flags::positive))
+               return step(arg);
+       
+       return power(step(arg), exp).hold();
+}
+
+static ex step_conjugate(const ex& arg)
+{
+       return step(arg);
+}
+
+REGISTER_FUNCTION(step, eval_func(step_eval).
+                        evalf_func(step_evalf).
+                        series_func(step_series).
+                        conjugate_func(step_conjugate).
+                        power_func(step_power));
+
 //////////
 // Complex sign
 //////////