Ticket #1173: trac_1173_add_complex_argument_erf.patch
File trac_1173_add_complex_argument_erf.patch, 5.6 KB (added by , 7 years ago) 


sage/functions/other.py
# HG changeset patch # User D. S. McNeil # Date 1298514253 28800 # Node ID 678841360c1b8902336e2138ca893236bbc5d7cf # Parent 8438b7c20d79c02a2ece3e1c3f7224a772ff8f07 Trac 1173: add complexargument erf diff r 8438b7c20d79 r 678841360c1b sage/functions/other.py
a b 24 24 one_half = ~SR(2) 25 25 26 26 class Function_erf(BuiltinFunction): 27 _eval_ = BuiltinFunction._eval_default28 27 def __init__(self): 29 28 r""" 30 29 The error function, defined as 31 30 `\text{erf}(x) = \frac{2}{\sqrt{\pi}} \int_0^x e^{t^2} dt`. 32 31 33 Sage currently only implements the error function (via a call to34 PARI) when the input is real.32 Sage implements the error function for both real and complex arguments 33 (via mpmath). 35 34 36 35 EXAMPLES:: 37 36 38 37 sage: erf(2) 39 38 erf(2) 40 39 sage: erf(2).n() 41 40 0.995322265018953 42 sage: loads(dumps(erf)) 43 erf 41 sage: erf(2).n(100) 42 0.99532226501895273416206925637 43 sage: erf(ComplexField(100)(2+3j)) 44 20.829461427614568389103088452 + 8.6873182714701631444280787545*I 45 sage: a = sqrt(pi)*I*erf(2*I)/2 46 sage: a 47 1/2*I*sqrt(pi)*erf(2*I) 48 sage: CC(a) 49 16.4526277655072 50 51 Note that erf(0) is immediately evaluated, but this behaviour 52 can be suppressed via the hold parameter, and then undone 53 via simplify: 44 54 45 The following fails because we haven't implemented 46 erf yet for complex values:: 47 48 sage: complex(erf(3*I)) 49 Traceback (most recent call last): 50 ... 51 TypeError: unable to simplify to complex approximation 55 sage: erf(0) 56 0 57 sage: erf(0,hold=True) 58 erf(0) 59 sage: simplify(erf(0,hold=True)) 60 0 52 61 53 TESTS: 62 63 TESTS:: 54 64 55 65 Check if conversion from maxima elements work:: 56 66 57 67 sage: merf = maxima(erf(x)).sage().operator() 58 68 sage: merf == erf 59 69 True 70 71 Make sure we can dump and load it: 72 73 sage: loads(dumps(erf(2))) 74 erf(2) 75 76 Check to make sure that exact ring inputs return unevaluated 77 (note that zero is an exception), that inexact rings evaluate, 78 and that everything returns an appropriate type: 79 80 sage: exact = SR, ZZ, QQ, int, long 81 sage: list(erf(ring(1)) for ring in exact) 82 [erf(1), erf(1), erf(1), erf(1), erf(1L)] 83 sage: erf(e), erf(pi) 84 (erf(e), erf(pi)) 85 sage: inexact = (RR, RealField(100), RDF, float, CC, ComplexField(100), CDF, complex) 86 sage: list(erf(ring(1)) for ring in inexact) 87 [0.842700792949715, 0.84270079294971486934122063508, 0.84270079295, 0.84270079294971489, 88 0.842700792949715, 0.84270079294971486934122063508, 0.84270079295, (0.84270079294971489+0j)] 89 sage: list(parent(ring(1)) == parent(erf(ring(1))) for ring in inexact) 90 [True, True, True, True, True, True, True, True] 91 92 Make sure that we can hold: 93 94 sage: erf(ComplexField(100)(2+3j),hold=True) 95 erf(2.0000000000000000000000000000 + 3.0000000000000000000000000000*I) 96 97 Check that largeprecision ComplexField inputs don't trigger an mpmath OverflowError 98 (strange bug while developing): 99 100 sage: CC(erf(ComplexField(1000)(2+3j))) 101 20.8294614276146 + 8.68731827147016*I 102 60 103 """ 61 104 BuiltinFunction.__init__(self, "erf", latex_name=r"\text{erf}") 62 105 106 def _eval_(self, x): 107 """ 108 EXAMPLES:: 109 110 sage: erf(1) 111 erf(1) 112 sage: erf(2.0) 113 0.995322265018953 114 115 TESTS:: 116 117 Test that trac #8983 is fixed  although it appears to have been fixed 118 by maximarelated changes, let's keep it that way: 119 120 sage: erf(0) 121 0 122 sage: solve(erf(x)==0,x) 123 [x == 0] 124 125 Verify we're returning the appropriate zero: 126 127 sage: erf(0) 128 0 129 sage: erf(0.0) 130 0.000000000000000 131 sage: erf(RealField(100)(0)) 132 0.00000000000000000000000000000 133 134 """ 135 if not isinstance(x, Expression) and is_inexact(x): 136 return self._evalf_(x, parent(x)) 137 if x == 0: 138 return parent(x)(0) 139 63 140 def _evalf_(self, x, parent=None): 64 141 """ 65 142 EXAMPLES:: … … 67 144 sage: erf(2).n() 68 145 0.995322265018953 69 146 sage: erf(2).n(150) 70 Traceback (most recent call last): 71 ... 72 NotImplementedError: erf not implemented for precision higher than 53 147 0.99532226501895273416206925636725292861089180 148 sage: erf(ComplexField(150)(2j)) 149 18.564802414575552598704291913241017198858002*I 150 73 151 """ 152 from mpmath import erf 74 153 try: 75 154 prec = parent.prec() 76 except AttributeError: # not a Sage parent 77 prec = 0 78 if prec > 53: 79 raise NotImplementedError, "erf not implemented for precision higher than 53" 80 return parent(1  pari(float(x)).erfc()) 81 155 except AttributeError: 156 prec = 53 157 return parent(mpmath_utils.call(erf, x, prec=prec)) 158 82 159 def _derivative_(self, x, diff_param=None): 83 160 """ 84 161 Derivative of erf function