# Need in solving a programm in FOTRAN

1. Feb 11, 2012

### Sampath Emani

Friends,
i have written a program in FOTRAN for solving a equation [f(x0,y0)= 2*(y**2)+5]
I'm in the learning stage of FOTRAN. So please don't mind if my program has got any silly mistakes.

program rungekutta

print *,' DIFFERENTIAL EQUATION WITH 1 VARIABLE OF ORDER 1'

print*,"enter the value of x0"

print*,"enter the value of y0"

print*,"enter the value of step size"

print*,"solution for the equation is",rk(x0,y0,h)

call runge(m,f1,n,h,x1)

end

function rk(y) result(r)

!Example: y'=(2*y^2+5)

real y,r

r = (2*(y**2)+5)
end function rk(y)

Subroutine runge(m,f1,n,h,x1)

integer f1,i,j,m,n,h

real x,w1,w2,w3,w4,x0,y;

do i=1, m
ni = (i - 1) * f1 - 1
do j=1, f1
x = x1 + h * (n + j)
w1 = h * f(x0,y0)
w2 = h * f(x0+h/2, y0+w1/2)
w3 = h * f(x0+h/2, y0+w2/2)
w4 = h * f(x0+h, y0+w3)
x = x0 + h

x = y + (w1 + w2 + w2 + w3 + w3 + w4) / 6

end do

end do

end

2. Feb 11, 2012

### gsal

what does the subroutine runge do for you? it is not being used anywhere.

why if function rk is declared with 1 argument, you pass 3 to it?

3. Feb 11, 2012

### Sampath Emani

yes sir,
i do agree. but I'm not able not correct that .
Can u help me in writing the correct step.
I took an equation (2*(y**2)+5)
i want to solve this using Runge kutta.

4. Mar 15, 2012

### Louisa

There are at least several problems that you need to rectify.
(In future, include all the error messages with your post, along with the
source.)

1. You need "IMPLICIT NONE" in the program and in each subroutine
and function.

2. What is "f"?

3. when you invoke rk, it is with 3 arguments.
Yet the function is defined with only one dummy argument.

4. You requested the input of "x0", but you read the value into "x", etc.