taylor sequence in c++

[Athar]

That's not a C++-related problem. The page tells you everything you need to know about fmod.

But well, since this probably ain't leading nowhere:
Add this line as the first line of your functions (you'll need to include cmath):
x=fmod(x,M_PI*2);

With that, you can reduce limit to something around 25.
Also, you need to use the double type for result and term as well, otherwise there'll be no difference.

[empror9]

many thanks man

it work correctly, for cos function it''s not that good but is sin id great!

double cos(double x) 
{ 
		x=fmod(x,M_PI*2);
        double result = 1;

        int limit = 20;
        int sign = -1;
        double last=1;

        for(int i=2 ; i<limit ; i+=2,sign=-sign)
        {
          last*=(x*x)/(i*(i-1));
          result += sign*last;
        }

        return result;

} 

in case x = 1.5708000

cos(x) = -3.67321e-006

in sample run cos(x) = -0.000000

one more Q,

now no need for the second forumla, am i right?


x=fmod(x,M_PI*2);
what is M_PI??

[Athar]

What do you mean, "it's not that great"?
cos(1.5708) is about -0.000003673205, which is exactly the result of the Taylor cos function.

Use the real cos function or a calculator to verify.

[empror9]

yes it's about -0.000000

but in the programme is cos(x) = -3.67321e-006 ,so it's not correct ((only in this case it shows a wrong result))

x=fmod(x,M_PI*2);
what is M_PI??

[Athar]

What are you going on about? -3.67321e-006 is equal to -0.00000367321.
M_PI is a macro constant for Pi that is defined in cmath.

[empror9]

i see,

thank you so much for your helping

thanks thanks

:)

[D80DSL3A]

The second formula is the one being used in the functions here. Your recent post for the cos() implements it on line #12. Methods based on both formulas were explored in this recent post: http://www.cplusplus.com/forum/general/26540/. Mind though what Athar has said about using arguments (values for x) that the series converges for. For the trig. series being considered this is -PI to +PI. You may expect values given outside this range to produce garbage for output!