R help - Jan 2004 - MATLAB to R

Ladies and Gentlemen,

In MATLAB, I can write:

for J=1:M
Y(J+1)=Y(J)+ h * feval(f,T(J),Y(J));
...

In R, I can write above as:

for (J in 2:M)
{
 y = y + h * f(t,y)
...
}
----
In MATLAB, I can write:

for J=1:M
k1 = feval(f,T(J),Y(J));
k2 = feval(f,T(J+1),Y(J)+ h * k1

How do I write k2 in R?
k1 = f(t,y)
k2 = ?

Thanks,
/oal

DivineSAAM at aol.com writes:
> In MATLAB, I can write:
>
> for J=1:M
> Y(J+1)=Y(J)+ h * feval(f,T(J),Y(J));
> ...
>
> In R, I can write above as:
>
> for (J in 2:M)
> {
>  y = y + h * f(t,y)
> ...
> }
Are you sure this gives the same result?  If Y and T in Matlab are
vectors, I believe

for (J in 1:M)
{
  y[J+1] <- y[J] + h * f(tt[J], y[J])
  ...
}

is what you want.  (Don't use `t' as a variable; t() is the function
to transpose a matrix.)
> for J=1:M
> k1 = feval(f,T(J),Y(J));
> k2 = feval(f,T(J+1),Y(J)+ h * k1
I assume you mean k1(J) = ... and k2(J) = ...
> How do I write k2 in R?
> k1 = f(t,y)
> k2 = ?
## If f can take vector arguments:
k1 <- f(tt[-M],y)
k2 <- f(tt[-1], y+h*k1)
## Otherwise:
for (J in 1:M) {
  k1[J] <- f(tt[J], y[J])
  k2[J] <- f(tt[J+1], y[J] + h*k1[J])
}

-- 
Hth,
Bj?rn-Helge Mevik