Hello friends,
I am new to Numerical Recipies Forum.
I am using it to evaluate a double integral of function f(x,y)=x(x+3y) where the limits of x,y are given [0,4]. I am modifying the method specified on page 164 of the book (FUNCTION quad3d ) for triple integration. It is working fine.
But I was wondering whether there is a way to evaluate the integral with the following limits:
1) x lies between 0 and 4.
2) y lies between 0 and x.
I am not able to figure out how to do this :(
Please help!
Thanks and Regards,
Arun Jotshi,
SUNY Buffalo,
USA.

Hello
I am a new member of Numerical Recipes Forum
I am using numerical recipes subroutines for calculation
my integral.
My integrand has strongly oscillatory behavior and singularity too. So, I have calculated it, but have obtained different results for any integration method. Now, I don’t really know which subroutine is correct for my integrand. Are there other methods for these types functions?
Thanks for your helps
Best regards,
Ghadir Mohammadkhani.

Facing the exact same problem as Arun Jotshi.
My function is similar to:

f(x,y)=x(x+3y)

Int x_0^4 Int y_0^x f(x,y) dy dx

(Would like to perform double integration numerically between the limits:

1) x lies between 0 and 4.
2) y lies between 0 and x.

Hope some one can direct me to the appropriate procedure for solving this.

Thanks in advance.

Friends,
Best is to call Maple 9 or higher using your C/C++ program to calculate the integrals. Hope this helps. It worked out for me.
Good Luck!
Arun.

i have resolve your probleme for double integral, you have a code file in this response, when i performe the double intergral.


! programme principale
!-------------------------------------------------------------------
external quad2d,qtrapx,qtrapy,qtrapz,y1,y2,z1,z2,func

x1=0.0
x2=4.0

call quad3d(x1,x2,ss)

pk=ss

write(6,*)pk

end

! subroutine qui calcul une integrale triple
!-------------------------------------------------------------------
subroutine quad2d(x1,x2,ss)
real ss,x1,x2,h
external h
call qgausx(h,x1,x2,ss)
return
end
function f(yy)
real f,yy,func,x,y
common /xy/ x,y
y=yy
f=func(x,y)
return
end
function h(xx)
real h,xx,f,y1,y2,x,y
external f
common /xy/ x,y
real ss
x=xx
call qgausy(f,y1(x),y2(x),ss)
h=ss
return
end


! LA fonction Ã* integrer
!---------------------------------------------------------------------

FUNCTION func(x,y)

func= x*(x+3*y)

RETURN

END

! LA fonction y1(x)
!---------------------------------------------------------------------

FUNCTION y1(x)

y1= 0*x

RETURN

END

! LA fonction y2(x)
!---------------------------------------------------------------------

FUNCTION y2(x)

y2= 1*x

RETURN

END

! INTEGRATION PAR LA METHODE DE GAUSS
!-----------------------------------------------------------------
SUBROUTINE qgausx(func,a,b,ss)
REAL a,b,ss,func
EXTERNAL func
INTEGER j
REAL dx,xm,xr,w(5),x(5)
SAVE W,x
DATA w/.2955242247,.2692667193,.2190863625,.149451349,.06 66713449/
DATA x/.1488743389,.4333953941,.6794095682,.8650633666,.9 739065285/
xm=0.5*(b+a)
xr=0.5*(b-a)
ss=0
do 11 j=1,5
dx=xr*x(j)
ss=ss+w(j)*(func(xm+dx)+func(xm-dx))
11 continue
ss=xr*ss
return
END


! INTEGRATION PAR LA METHODE DE GAUSS

SUBROUTINE qgausy(func,a,b,ss)
REAL a,b,ss,func
EXTERNAL func
INTEGER j
REAL dx,xm,xr,w(5),x(5)
SAVE W,x
DATA w/.2955242247,.2692667193,.2190863625,.149451349,.06 66713449/
DATA x/.1488743389,.4333953941,.6794095682,.8650633666,.9 739065285/
xm=0.5*(b+a)
xr=0.5*(b-a)
ss=0
do 11 j=1,5
dx=xr*x(j)
ss=ss+w(j)*(func(xm+dx)+func(xm-dx))
11 continue
ss=xr*ss
return
END

! INTEGRATION PAR LA METHODE DE GAUSS

SUBROUTINE qgausz(func,a,b,ss)
REAL a,b,ss,func
EXTERNAL func
INTEGER j
REAL dx,xm,xr,w(5),x(5)
SAVE W,x
DATA w/.2955242247,.2692667193,.2190863625,.149451349,.06 66713449/
DATA x/.1488743389,.4333953941,.6794095682,.8650633666,.9 739065285/
xm=0.5*(b+a)
xr=0.5*(b-a)
ss=0
do 11 j=1,5
dx=xr*x(j)
ss=ss+w(j)*(func(xm+dx)+func(xm-dx))
11 continue
ss=xr*ss
return
END




have fine.