X-Git-Url: https://www.ginac.de/ginac.git//ginac.git?p=ginac.git;a=blobdiff_plain;f=ginac%2Finifcns_gamma.cpp;h=ecec37a603dbc208f12aeacb790a2daac18b6309;hp=7bd6669bb8b5eb8c817fd016718c5e3bfdaa2546;hb=721cff7b2f8d555e085202f6f3f47801b92d0413;hpb=8d16780dbd9f4da9397e638aca213745589818c0

diff --git a/ginac/inifcns_gamma.cpp b/ginac/inifcns_gamma.cpp
index 7bd6669b..ecec37a6 100644
--- a/ginac/inifcns_gamma.cpp
+++ b/ginac/inifcns_gamma.cpp
@@ -1,6 +1,7 @@
 /** @file inifcns_gamma.cpp
  *
- *  Implementation of Gamma function and some related stuff. */
+ *  Implementation of Gamma-function, Beta-function, Polygamma-functions, and
+ *  some related stuff. */
 
 /*
  *  GiNaC Copyright (C) 1999 Johannes Gutenberg University Mainz, Germany
@@ -26,45 +27,58 @@
 #include "inifcns.h"
 #include "ex.h"
 #include "constant.h"
+#include "series.h"
 #include "numeric.h"
 #include "power.h"
+#include "relational.h"
 #include "symbol.h"
+#include "utils.h"
 
+#ifndef NO_GINAC_NAMESPACE
 namespace GiNaC {
+#endif // ndef NO_GINAC_NAMESPACE
 
 //////////
-// gamma function
+// Gamma-function
 //////////
 
+static ex gamma_evalf(ex const & x)
+{
+    BEGIN_TYPECHECK
+        TYPECHECK(x,numeric)
+    END_TYPECHECK(gamma(x))
+    
+    return gamma(ex_to_numeric(x));
+}
+
 /** Evaluation of gamma(x). Knows about integer arguments, half-integer
  *  arguments and that's it. Somebody ought to provide some good numerical
  *  evaluation some day...
  *
- *  @exception fail_numeric("complex_infinity") or something similar... */
+ *  @exception std::domain_error("gamma_eval(): simple pole") */
 static ex gamma_eval(ex const & x)
 {
     if (x.info(info_flags::numeric)) {
-
         // trap integer arguments:
-        if ( x.info(info_flags::integer) ) {
+        if (x.info(info_flags::integer)) {
             // gamma(n+1) -> n! for postitive n
-            if ( x.info(info_flags::posint) ) {
+            if (x.info(info_flags::posint)) {
                 return factorial(ex_to_numeric(x).sub(numONE()));
             } else {
-                return numZERO();  // Infinity. Throw? What?
+                throw (std::domain_error("gamma_eval(): simple pole"));
             }
         }
         // trap half integer arguments:
-        if ( (x*2).info(info_flags::integer) ) {
-            // trap positive x=(n+1/2)
+        if ((x*2).info(info_flags::integer)) {
+            // trap positive x==(n+1/2)
             // gamma(n+1/2) -> Pi^(1/2)*(1*3*..*(2*n-1))/(2^n)
-            if ( (x*2).info(info_flags::posint) ) {
+            if ((x*2).info(info_flags::posint)) {
                 numeric n = ex_to_numeric(x).sub(numHALF());
                 numeric coefficient = doublefactorial(n.mul(numTWO()).sub(numONE()));
                 coefficient = coefficient.div(numTWO().power(n));
                 return coefficient * pow(Pi,numHALF());
             } else {
-                // trap negative x=(-n+1/2)
+                // trap negative x==(-n+1/2)
                 // gamma(-n+1/2) -> Pi^(1/2)*(-2)^n/(1*3*..*(2*n-1))
                 numeric n = abs(ex_to_numeric(x).sub(numHALF()));
                 numeric coefficient = numeric(-2).power(n);
@@ -75,50 +89,154 @@ static ex gamma_eval(ex const & x)
     }
     return gamma(x).hold();
 }    
+
+static ex gamma_diff(ex const & x, unsigned diff_param)
+{
+    GINAC_ASSERT(diff_param==0);
     
-static ex gamma_evalf(ex const & x)
+    return psi(x)*gamma(x);  // diff(log(gamma(x)),x)==psi(x)
+}
+
+static ex gamma_series(ex const & x, symbol const & s, ex const & point, int order)
+{
+    // method:
+    // Taylor series where there is no pole falls back to psi functions.
+    // On a pole at -n use the identity
+    //   series(GAMMA(x),x=-n,order) ==
+    //   series(GAMMA(x+n+1)/(x*(x+1)...*(x+n)),x=-n,order+1);
+    ex xpoint = x.subs(s==point);
+    if (!xpoint.info(info_flags::integer) || xpoint.info(info_flags::positive))
+        throw do_taylor();
+    // if we got here we have to care for a simple pole at -n:
+    numeric n = -ex_to_numeric(xpoint);
+    ex ser_numer = gamma(x+n+exONE());
+    ex ser_denom = exONE();
+    for (numeric p; p<=n; ++p)
+        ser_denom *= x+p;
+    return (ser_numer/ser_denom).series(s, point, order+1);
+}
+
+REGISTER_FUNCTION(gamma, gamma_eval, gamma_evalf, gamma_diff, gamma_series);
+
+//////////
+// Beta-function
+//////////
+
+static ex beta_evalf(ex const & x, ex const & y)
 {
     BEGIN_TYPECHECK
         TYPECHECK(x,numeric)
-    END_TYPECHECK(gamma(x))
+        TYPECHECK(y,numeric)
+    END_TYPECHECK(beta(x,y))
     
-    return gamma(ex_to_numeric(x));
+    return gamma(ex_to_numeric(x))*gamma(ex_to_numeric(y))
+        / gamma(ex_to_numeric(x+y));
 }
 
-static ex gamma_diff(ex const & x, unsigned diff_param)
+static ex beta_eval(ex const & x, ex const & y)
 {
-    ASSERT(diff_param==0);
-
-    return psi(exZERO(),x)*gamma(x);
+    if (x.info(info_flags::numeric) && y.info(info_flags::numeric)) {
+        numeric nx(ex_to_numeric(x));
+        numeric ny(ex_to_numeric(y));
+        // treat all problematic x and y that may not be passed into gamma,
+        // because they would throw there although beta(x,y) is well-defined:
+        if (nx.is_real() && nx.is_integer() &&
+            ny.is_real() && ny.is_integer()) {
+            if (nx.is_negative()) {
+                if (nx<=-ny)
+                    return numMINUSONE().power(ny)*beta(1-x-y, y);
+                else
+                    throw (std::domain_error("beta_eval(): simple pole"));
+            }
+            if (ny.is_negative()) {
+                if (ny<=-nx)
+                    return numMINUSONE().power(nx)*beta(1-y-x, x);
+                else
+                    throw (std::domain_error("beta_eval(): simple pole"));
+            }
+            return gamma(x)*gamma(y)/gamma(x+y);
+        }
+        // no problem in numerator, but denominator has pole:
+        if ((nx+ny).is_real() &&
+            (nx+ny).is_integer() &&
+            !(nx+ny).is_positive())
+            return exZERO();
+        return gamma(x)*gamma(y)/gamma(x+y);
+    }
+    return beta(x,y).hold();
 }
 
-static ex gamma_series(ex const & x, symbol const & s, ex const & point, int order)
+static ex beta_diff(ex const & x, ex const & y, unsigned diff_param)
 {
-	// FIXME: Only handle one special case for now...
-	if (x.is_equal(s) && point.is_zero()) {
-		ex e = 1 / s - EulerGamma + s * (pow(Pi, 2) / 12 + pow(EulerGamma, 2) / 2) + Order(pow(s, 2));
-		return e.series(s, point, order);
-	} else
-		throw(std::logic_error("don't know the series expansion of this particular gamma function"));
+    GINAC_ASSERT(diff_param<2);
+    ex retval;
+    
+    if (diff_param==0)  // d/dx beta(x,y)
+        retval = (psi(x)-psi(x+y))*beta(x,y);
+    if (diff_param==1)  // d/dy beta(x,y)
+        retval = (psi(y)-psi(x+y))*beta(x,y);
+    return retval;
 }
 
-REGISTER_FUNCTION(gamma, gamma_eval, gamma_evalf, gamma_diff, gamma_series);
+REGISTER_FUNCTION(beta, beta_eval, beta_evalf, beta_diff, NULL);
 
 //////////
-// psi function (aka polygamma function)
+// Psi-function (aka polygamma-function)
 //////////
 
-/** Evaluation of polygamma-function psi(n,x). 
+static ex psi1_evalf(ex const & x)
+{
+    BEGIN_TYPECHECK
+        TYPECHECK(x,numeric)
+    END_TYPECHECK(psi(x))
+    
+    return psi(ex_to_numeric(x));
+}
+
+/** Evaluation of polygamma-function psi(x). 
  *  Somebody ought to provide some good numerical evaluation some day... */
-static ex psi_eval(ex const & n, ex const & x)
+static ex psi1_eval(ex const & x)
 {
-    if (n.info(info_flags::numeric) && x.info(info_flags::numeric)) {
-        // do some stuff...
+    if (x.info(info_flags::numeric)) {
+        if (x.info(info_flags::integer) && !x.info(info_flags::positive))
+            throw (std::domain_error("psi_eval(): simple pole"));
+        if (x.info(info_flags::positive)) {
+            // psi(n) -> 1 + 1/2 +...+ 1/(n-1) - EulerGamma
+            if (x.info(info_flags::integer)) {
+                numeric rat(0);
+                for (numeric i(ex_to_numeric(x)-numONE()); i.is_positive(); --i)
+                    rat += i.inverse();
+                return rat-EulerGamma;
+            }
+            // psi((2m+1)/2) -> 2/(2m+1) + 2/2m +...+ 2/1 - EulerGamma - 2log(2)
+            if ((exTWO()*x).info(info_flags::integer)) {
+                numeric rat(0);
+                for (numeric i((ex_to_numeric(x)-numONE())*numTWO()); i.is_positive(); i-=numTWO())
+                    rat += numTWO()*i.inverse();
+                return rat-EulerGamma-exTWO()*log(exTWO());
+            }
+            if (x.compare(exONE())==1) {
+                // should call numeric, since >1
+            }
+        }
     }
-    return psi(n, x).hold();
-}    
+    return psi(x).hold();
+}
+
+static ex psi1_diff(ex const & x, unsigned diff_param)
+{
+    GINAC_ASSERT(diff_param==0);
     
-static ex psi_evalf(ex const & n, ex const & x)
+    return psi(exONE(), x);
+}
+
+const unsigned function_index_psi1 = function::register_new("psi", psi1_eval, psi1_evalf, psi1_diff, NULL);
+
+//////////
+// Psi-functions (aka polygamma-functions)  psi(0,x)==psi(x)
+//////////
+
+static ex psi2_evalf(ex const & n, ex const & x)
 {
     BEGIN_TYPECHECK
         TYPECHECK(n,numeric)
@@ -128,18 +246,40 @@ static ex psi_evalf(ex const & n, ex const & x)
     return psi(ex_to_numeric(n), ex_to_numeric(x));
 }
 
-static ex psi_diff(ex const & n, ex const & x, unsigned diff_param)
+/** Evaluation of polygamma-function psi(n,x). 
+ *  Somebody ought to provide some good numerical evaluation some day... */
+static ex psi2_eval(ex const & n, ex const & x)
 {
-    ASSERT(diff_param==0);
-    
-    return psi(n+1, x);
-}
+    // psi(0,x) -> psi(x)
+    if (n.is_zero())
+        return psi(x);
+    // psi(-1,x) -> log(gamma(x))
+    if (n.is_equal(exMINUSONE()))
+        return log(gamma(x));
+    if (n.info(info_flags::numeric) && n.info(info_flags::posint) &&
+        x.info(info_flags::numeric)) {
+        numeric nn = ex_to_numeric(n);
+        numeric nx = ex_to_numeric(x);
+        if (x.is_equal(exONE()))
+            return numMINUSONE().power(nn+numONE())*factorial(nn)*zeta(ex(nn+numONE()));
+    }
+    return psi(n, x).hold();
+}    
 
-static ex psi_series(ex const & n, ex const & x, symbol const & s, ex const & point, int order)
+static ex psi2_diff(ex const & n, ex const & x, unsigned diff_param)
 {
-    throw(std::logic_error("Nobody told me how to series expand the psi function. :-("));
+    GINAC_ASSERT(diff_param<2);
+    
+    if (diff_param==0) {
+        // d/dn psi(n,x)
+        throw(std::logic_error("cannot diff psi(n,x) with respect to n"));
+    }
+    // d/dx psi(n,x)
+    return psi(n+1, x);
 }
 
-REGISTER_FUNCTION(psi, psi_eval, psi_evalf, psi_diff, psi_series);
+const unsigned function_index_psi2 = function::register_new("psi", psi2_eval, psi2_evalf, psi2_diff, NULL);
 
+#ifndef NO_GINAC_NAMESPACE
 } // namespace GiNaC
+#endif // ndef NO_GINAC_NAMESPACE