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# sym_operations.cpp

    00001 /*
    00002  *             Copyright (C) 2005 Maarten Keijzer
    00003  *
    00004  *          This program is free software; you can redistribute it and/or modify
    00005  *          it under the terms of version 2 of the GNU General Public License as
    00006  *          published by the Free Software Foundation.
    00007  *
    00008  *          This program is distributed in the hope that it will be useful,
    00009  *          but WITHOUT ANY WARRANTY; without even the implied warranty of
    00010  *          MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    00011  *          GNU General Public License for more details.
    00012  *
    00013  *          You should have received a copy of the GNU General Public License
    00014  *          along with this program; if not, write to the Free Software
    00015  *          Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    00016  */
    00017
    00018 #include <FunDef.h>
    00019
    00020 using namespace std;
    00021
    00022 Sym simplify_constants(Sym sym) {
    00023
    00024     SymVec args = sym.args();
    00025     token_t token = sym.token();
    00026
    00027     bool has_changed = false;
    00028     bool all_constants = true;
    00029
    00030     for (unsigned i = 0; i < args.size(); ++i) {
    00031
    00032         Sym arg = simplify_constants(args[i]);
    00033
    00034         if (arg != args[i]) {
    00035             has_changed = true;
    00036         }
    00037         args[i] = arg;
    00038
    00039         all_constants &= is_constant(args[i].token());
    00040     }
    00041
    00042     if (args.size() == 0) {
    00043
    00044         if (sym.token() == sum_token) return SymConst(0.0);
    00045         if (sym.token() == prod_token) return SymConst(1.0);
    00046
    00047         return sym; // variable or constant
    00048     }
    00049
    00050     if (all_constants) {
    00051         // evaluate
    00052
    00053         vector<double> dummy;
    00054
    00055         double v = ::eval(sym, dummy);
    00056
    00057         Sym result = SymConst(v);
    00058
    00059         return result;
    00060     }
    00061
    00062     if (has_changed) {
    00063         return Sym(token, args);
    00064     }
    00065
    00066     return sym;
    00067
    00068 }
    00069
    00070 // currently only simplifies constants
    00071 Sym simplify(Sym sym) {
    00072
    00073     return simplify_constants(sym);
    00074
    00075 }
    00076
    00077 Sym derivative(token_t token, Sym x) {
    00078     Sym one = Sym(prod_token);
    00079
    00080     switch (token) {
    00081         case inv_token : return Sym(inv_token, sqr(x));
    00082
    00083         case sin_token : return -cos(x);
    00084         case cos_token : return sin(x);
    00085         case tan_token : return one + sqr(tan(x));
    00086
    00087         case asin_token : return inv( sqrt(one - sqr(x)));
    00088         case acos_token:  return -inv( sqrt(one - sqr(x)));
    00089         case atan_token : return inv( sqrt(one + sqr(x)));
    00090
    00091         case cosh_token : return -sinh(x);
    00092         case sinh_token : return cosh(x);
    00093         case tanh_token : return one - sqr( tanh(x) );
    00094
    00095         case asinh_token : return inv( sqrt( one + sqr(x) ));
    00096         case acosh_token : return inv( sqrt(x-one) * sqrt(x + one)  );
    00097         case atanh_token : return inv(one - sqr(x));
    00098
    00099         case exp_token : return exp(x);
    00100         case log_token : return inv(x);
    00101
    00102         case sqr_token : return SymConst(2.0) * x;
    00103         case sqrt_token : return SymConst(0.5) * inv( sqrt(x));
    00104         default :
    00105             throw differentiation_error();
    00106     }
    00107
    00108     return x;
    00109 }
    00110
    00111 extern Sym differentiate(Sym sym, token_t dx) {
    00112
    00113     token_t token = sym.token();
    00114
    00115     Sym zero = Sym(sum_token);
    00116     Sym one  = Sym(prod_token);
    00117
    00118     if (token == dx) {
    00119         return one;
    00120     }
    00121
    00122     SymVec args = sym.args();
    00123
    00124     if (args.size() == 0) { // df/dx with f != x
    00125         return zero;
    00126     }
    00127
    00128     switch (token) {
    00129
    00130         case sum_token:
    00131             {
    00132                 for (unsigned i = 0; i < args.size(); ++i) {
    00133                     args[i] = differentiate(args[i], dx);
    00134                 }
    00135
    00136                 if (args.size() == 1) return args[0];
    00137                 return Sym(sum_token, args);
    00138             }
    00139         case min_token :
    00140             {
    00141                 return -differentiate(args[0],dx);
    00142             }
    00143         case prod_token:
    00144             {
    00145                 if (args.size() == 1) return differentiate(args[0], dx);
    00146
    00147                 if (args.size() == 2) {
    00148                     return args[0] * differentiate(args[1], dx) + args[1] * differentiate(args[0], dx);
    00149                 }
    00150                 // else
    00151                 Sym c = args.back();
    00152                 args.pop_back();
    00153                 Sym f = Sym(prod_token, args);
    00154                 Sym df = differentiate( f, dx);
    00155
    00156                 return c * df + f * differentiate(c,dx);
    00157             }
    00158         case pow_token :
    00159             {
    00160                 return pow(args[0], args[1]) * args[1] * inv(args[0]);
    00161             }
    00162         case ifltz_token :
    00163             { // cannot be differentiated
    00164                 throw differentiation_error(); // TODO define proper exception
    00165             }
    00166
    00167         default: // unary function: apply chain rule
    00168             {
    00169                 Sym arg = args[0];
    00170                 return derivative(token, arg) * differentiate(arg, dx);
    00171             }
    00172     }
    00173
    00174 }