Arctg table!
Author
Anyone could past here, a harcoded Arctg table as array of 360 entries?
Would apreciate your help!
Thanks.
DIY:
Output.
EDIT:
Did you want atan, tan or 1 / tan?
[Edited by - _fastcall on August 3, 2009 3:11:01 PM]
-- lua5.1local f = assert( io.open( "invtan.txt", "w" ) )for i=0, 360 do f:write( 1 / math.tan( i * math.pi / 180 ) .. ' ' )endOutput.
EDIT:
Did you want atan, tan or 1 / tan?
[Edited by - _fastcall on August 3, 2009 3:11:01 PM]
surely you could make that list yourself via a program? :P
shouldnt be too hard, esp not for someone who knows asm (;
shouldnt be too hard, esp not for someone who knows asm (;
Author
Quote:Original post by alvaro
Do you mean a table with the tangent of each angle that is an integer number of degrees?
I mean the Arc tangent values for the selected angle entry, so ArcTg[0] will store the ArcTg value of angle 0, and ArcTg[359] will store the ArcTg value of angle 259.
See, I have a circle(x0,y0), a point in the circle(x,y).
What I want to do is to detrmine the angle with this formula:
Angle= ArcTg (y-y0/x-x0)
so with the lookup table I can simply do this to get the angle:
float Angle= ArcTgArray[(y-y0/x-x0)];Thanks.
But that slope will not always be in [0,360]... You can't have a table that covers all the reals. You could have a table for values between 0 and 1 (in however many steps you want) and reduce all the other cases to this one. Could that be roughly what you want?
const int step = 361;double arctan[step];// Create a table that uses values from -1 to 1for ( int i = 0; i < step; ++i ) arctan = std::atan( (double)(i*2 - step) / (double)step );// Then:double angle = arctan[ std::min( step-1, std::max( 0, (int)( (test * step + step)/2 ) ) ) ];You should be using atan2( y-y0, x-x0 ) anyways ...
If you don't have atan2, you can use something like this:
double atan2(double y, double x) { double alpha=3.141592653589793238462643383279; double gx=-1.0, gy=0.0, result=-alpha; static double cosine_and_sine[32][2]={ {-1,0}, {0,1}, {0.70710678118654757274,0.70710678118654746172}, {0.92387953251128673848,0.38268343236508978178}, {0.98078528040323043058,0.19509032201612824808}, {0.99518472667219692873,0.098017140329560603629}, {0.99879545620517240501,0.049067674327418014935}, {0.99969881869620424997,0.024541228522912288124}, {0.99992470183914450299,0.012271538285719925387}, {0.99998117528260110909,0.0061358846491544752691}, {0.99999529380957619118,0.0030679567629659761432}, {0.99999882345170187925,0.0015339801862847655001}, {0.99999970586288222663,0.0007669903187427044855}, {0.99999992646571789212,0.00038349518757139556321}, {0.99999998161642933425,0.00019174759731070329153}, {0.99999999540410733356,9.5873799095977344669e-05}, {0.99999999885102686115,4.793689960306688131e-05}, {0.99999999971275665978,2.3968449808418219318e-05}, {0.99999999992818922046,1.1984224905069705298e-05}, {0.9999999999820472496,5.9921124526424275272e-06}, {0.9999999999955118124,2.9960562263346608352e-06}, {0.99999999999887800861,1.4980281131690111427e-06}, {0.99999999999971944664,7.490140565847157414e-07}, {0.9999999999999298339,3.7450702829238412872e-07}, {0.99999999999998245848,1.8725351414619534661e-07}, {0.99999999999999567013,9.3626757073098083589e-08}, {0.99999999999999888978,4.6813378536549088116e-08}, {0.99999999999999977796,2.3406689268274550676e-08}, {0.99999999999999988898,1.1703344634137276992e-08}, {1,5.8516723170686384961e-09}, {1,2.925836158534319248e-09}, {1,1.462918079267159624e-09} }; for(int i=0;i<32;++i) { double c=cosine_and_sine[0], s=cosine_and_sine[1]; double nx=gx*c-gy*s, ny=gy*c+gx*s; if(x*ny<y*nx) { result += alpha; gx=nx; gy=ny; } alpha*=.5; } return result;}
Author
@alvaro: I can have only 360 array's entry, and then check for the nearest array value to the value i got from calculating x-x0/y-y0.
@_fastcall: Could you please provide me with the output as you did in your first post? My environement compiler does not have a math library (no cos, sin... functions) and I cannot install other compilers.
Thanks.
@_fastcall: Could you please provide me with the output as you did in your first post? My environement compiler does not have a math library (no cos, sin... functions) and I cannot install other compilers.
Thanks.
Program:
The output:
Output.
You can use the binary interpreters that come with lua or python to generate your tables for you, as shown in my first post.
#include <iterator>#include <fstream>#include <iomanip>#include <cmath>int main(){ const int step = 361; double arctan[step]; // Note: Range is from -1 to 1 inclusive. for ( int i = 0; i < step; ++i ) arctan = std::atan( (double)(i*2 - step) / (double)(step-1) ); std::ofstream fs( "out.txt" ); fs.precision( 16 ); std::copy( arctan, arctan + step, std::ostream_iterator<double>( fs, " " ) ); fs.flush();}The output:
Output.
You can use the binary interpreters that come with lua or python to generate your tables for you, as shown in my first post.
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