[R] Looping matrix multiplication

[wilkesma]

I am dealing with a number of time-series consisting of 2250 samples of flow
velocity in 2D (Vx, Vy).

For each time-series I have determined the resultant vector angle (d) and
magnitude (Vres) based on the ensemble means of Vx and Vy and now want to
rotate each point in the time-series by d so that mean(Vx)=Vres and
mean(Vy)=0.

Here is the code I have written to perform the rotation for a single
time-step:

n <- 2250 #number of samples in time series
R <- matrix ((c ((cos(d)), (-sin(d)), (sin(d)), (cos(d)))), 2) #rotation
matrix, where d is the resultant vector angle in degrees
V <- t (matrix ((c (Vx, Vy)), n)) #velocity matrix
Vadj <- R %*% (V) [, 1] #e.g. for the first Vx, Vy pair in the time-series

Now what I want to do is loop this to give me the solution at each time-step
and then append the adjusted Vx and Vy time-series to a new matrix.  Can
someone please suggest how I should about this?

Thanks,
Martin



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