Doubt about formula transcription
in [Fortran]
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From: robin on 12 Apr 2008 10:45 "Leonardo Marques" <surf3r0(a)gmail.com> wrote in message news:9c4bdee7-084e-4644-8b90-74cbef524878(a)u3g2000hsc.googlegroups.com... > hey guys, > > im with a little problem when im transcripting a math formula from > maple to fortran, because when i put a solution on the equation, i got > a result diferent from zero. > > The formula is: 2*arctan(sin(a)*cos(a)/(.8-cos(a)^2))-4/9*Pi ; > I've transcripted to fortran as: 2*atan((sin(a)*cos(a))/(0.8- > cos(a)**2))-((pi)*4/9) > > There's correct?! > a piece of my code: You need the statement IMPLICIT NONE after the FUNCTION statement (and in all other procedures). That will reveal errors of the kind that you made in the code.
From: e p chandler on 4 May 2008 22:30 On Apr 7, 3:36 pm, Leonardo Marques <surf...(a)gmail.com> wrote: > hey guys, > > im with a little problem when im transcripting a mathformulafrom > maple to fortran, because when i put a solution on the equation, i got > a result diferent from zero. > > Theformulais: 2*arctan(sin(a)*cos(a)/(.8-cos(a)^2))-4/9*Pi ; > I've transcripted to fortran as: 2*atan((sin(a)*cos(a))/(0.8- > cos(a)**2))-((pi)*4/9) [code snipped] Your equation has closed form solutions. let gamma=(2pi)/9 1. invert the equation 2. apply formulas for sin(2x) and cos(2x) sin(2a) sin(gamma) ---------- = tan(gamma) = ---------- .6-cos(2a) cos(gamma) 3. cross multiply and simplify sin(2a) cos(gamma) + cos(2a) sin(gamma) = .6 sin(gamma) 4. apply formula for sin(A+B) sin(2a+gamma) = .6 sin(gamma) 5. let beta = arcsine(.6 sin(gamma)) note that sin(x) = sin(pi-x) 2x + gamma = beta pi - (2y + gamma) = beta solve for principal solutions x and y = (beta-gamma)/2 and (pi-beta-gamma)/2 [other solutions can of course be obtained by adding or subtracting multiples of 2pi above.] - e
From: glen herrmannsfeldt on 4 May 2008 22:55 On Apr 7, 3:36 pm, Leonardo Marques <surf...(a)gmail.com> wrote: > I've transcripted to fortran as: 2*atan((sin(a)*cos(a))/(0.8- > cos(a)**2))-((pi)*4/9) I would use atan2(sin(a)*cos(a),0.8-cos(a)**2)-pi*4/9 You might also want it in double precision. Likely it won't come out exactly zero, but should be close if a is close to a solution. -- glen
From: Terence on 4 May 2008 23:50
On May 5, 12:55 pm, glen herrmannsfeldt <g...(a)ugcs.caltech.edu> wrote: > On Apr 7, 3:36 pm, Leonardo Marques <surf...(a)gmail.com> wrote: > > > I've transcripted to fortran as: 2*atan((sin(a)*cos(a))/(0.8- > > cos(a)**2))-((pi)*4/9) > > I would use atan2(sin(a)*cos(a),0.8-cos(a)**2)-pi*4/9 > > You might also want it in double precision. Likely it won't > come out exactly zero, but should be close if a is close > to a solution. > > -- glen Small typo there Glen (and biy, do I make them with this small type face). Should be atan2(sin(a)*cos(a)/0.8-cos(a)**2)-pi*4/9 And I would still prefer seeing that 4/9 as 4.0/9.0 ! |