Alfredo_MF - 1 year ago 67
R Question

# Multiply recursiverly in r

Having the following matrix and vector.

``````x<-matrix(c(1,4,7,
2,5,8,
3,6,9), nrow = 3)
w <- c(1,1,1)
res <- c()
``````

What is the best way to multiply recursiverly till obtain a desire sum of the results as exemplified:

``````res[1]<-w %*%x[1,]
res[2]<-w %*%x[2,]
res[3]<-w %*%x[3,]
res[4]<-w %*%x[1,]
res[5]<-w %*%x[2,]

sum(res)>1000 #Multiply recursiverly till the sum of the results sum(res) goes further than 1000.
``````

Here is how to do it recursively:

``````f <- function(x, w, res){
if (sum(res)>1000)
return(res)
res <- c(res, x%*%w)
f(x,w,res)
}
``````

Call it with your pre-defined objects. That is:

``````f(x, w, res)
``````

Which will give you:

``````# [1]  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6 15 24  6
# [62] 15 24  6 15 24  6 15 24
``````
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