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69 lines
1.7 KiB
Go
69 lines
1.7 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package math
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/*
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* floating-point arctangent
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*
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* atan returns the value of the arctangent of its
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* argument in the range [-pi/2,pi/2].
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* there are no error returns.
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* coefficients are #5077 from Hart & Cheney. (19.56D)
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*/
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const
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(
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ap4 = .161536412982230228262e2;
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ap3 = .26842548195503973794141e3;
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ap2 = .11530293515404850115428136e4;
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ap1 = .178040631643319697105464587e4;
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ap0 = .89678597403663861959987488e3;
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aq4 = .5895697050844462222791e2;
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aq3 = .536265374031215315104235e3;
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aq2 = .16667838148816337184521798e4;
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aq1 = .207933497444540981287275926e4;
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aq0 = .89678597403663861962481162e3;
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apio2 = .15707963267948966192313216e1;
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apio4 = .7853981633974483096156608e0;
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asq2p1 = .2414213562373095048802e1; // sqrt(2)+1
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asq2m1 = .414213562373095048802e0; // sqrt(2)-1
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)
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/*
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* xatan evaluates a series valid in the
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* range [-0.414...,+0.414...]. (tan(pi/8))
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*/
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func xatan(arg float64) float64 {
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argsq := arg*arg;
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value := ((((ap4*argsq + ap3)*argsq + ap2)*argsq + ap1)*argsq + ap0);
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value = value/(((((argsq + aq4)*argsq + aq3)*argsq + aq2)*argsq + aq1)*argsq + aq0);
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return value*arg;
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}
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/*
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* satan reduces its argument (known to be positive)
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* to the range [0,0.414...] and calls xatan.
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*/
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func satan(arg float64) float64 {
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if arg < asq2m1 {
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return xatan(arg);
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}
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if arg > asq2p1 {
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return apio2 - xatan(1/arg);
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}
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return apio4 + xatan((arg-1)/(arg+1));
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}
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/*
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* atan makes its argument positive and
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* calls the inner routine satan.
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*/
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export func Atan(arg float64) float64 {
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if arg > 0 {
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return satan(arg);
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}
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return -satan(-arg);
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}
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