Hi
i am having a problem with the 'integrate' function
the function i want to integrate has the form
sum(vector^x)
i have defined the function with a for loop first -
integrandtotest <- function(x)
{a<-rep(0,len=2)
for (i in 1:2)
{a[i]<-t[i]^x}
sum(a)
}
the results gives errors
###########
Error in integrate(integrandtotest, lower = 0.1, upper = 2,
subdivisions = 10000) :
evaluation of function gave a result of wrong length
In addition: Warning messages:
1: number of items to replace is not a multiple of replacement
length
2: number of items to replace is not a multiple of replacement
length
#######
I then tried a vector multiplication instead of the for loop
integrandtotest3 <- function(x)
{b<-c(t[1],t[2])
a<-b^x
sum(a)
}
which gave errors
########
Error in integrate(integrandtotest3, lower = 0.1, upper = 2,
subdivisions = 10000) :
evaluation of function gave a result of wrong length
In addition: Warning message:
longer object length
is not a multiple of shorter object length in: b^x
##########
but when i write the functio out long-hand as follows:
integrandtotest2 <- function(x)
{t[1]^x+t[2]^x}
the integrate function works perfectly.......
###> integralresulttotest2<-integrate(integrandtotest2, lower=0.1,
upper=2, subdivisions=10000)> integralresulttotest2
1.642369 with absolute error < 1.8e-14
###
Unfortunatley my real life example has the vector a with length at
least 100.
Is the any way round these errors?
Many thanks for answers to my first question to this list
yours
Alan
Alan Brennan
Director of Health Economics and Decision Science
http://www.shef.ac.uk/scharr/sections/heds
ScHARR
School of Health and Related Research
University of Sheffield
Regent Ct
30 Regent St
Sheffield S1 4DA
Tel:+44 (0)114 2220684
Fax:+44 (0)114 2724095
e-mail:a.brennan at sheffield.ac.uk
A.Brennan wrote:> Hi > > i am having a problem with the 'integrate' function > the function i want to integrate has the form > sum(vector^x) > > i have defined the function with a for loop first - > integrandtotest <- function(x) > {a<-rep(0,len=2) > for (i in 1:2) > {a[i]<-t[i]^x} > sum(a) > } > > the results gives errors > ########### > Error in integrate(integrandtotest, lower = 0.1, upper = 2, > subdivisions = 10000) : > evaluation of function gave a result of wrong length > In addition: Warning messages: > 1: number of items to replace is not a multiple of replacement > length > 2: number of items to replace is not a multiple of replacement > length > ####### > > I then tried a vector multiplication instead of the for loop > > > integrandtotest3 <- function(x) > {b<-c(t[1],t[2]) > a<-b^x > sum(a) > } > > which gave errors > ######## > Error in integrate(integrandtotest3, lower = 0.1, upper = 2, > subdivisions = 10000) : > evaluation of function gave a result of wrong length > In addition: Warning message: > longer object length > is not a multiple of shorter object length in: b^x > ########## > > but when i write the functio out long-hand as follows: > > integrandtotest2 <- function(x) > {t[1]^x+t[2]^x} > > the integrate function works perfectly....... > ### > >>integralresulttotest2<-integrate(integrandtotest2, lower=0.1, > > upper=2, subdivisions=10000) > >>integralresulttotest2 > > 1.642369 with absolute error < 1.8e-14 > ### > > Unfortunatley my real life example has the vector a with length at > least 100. > > Is the any way round these errors? > > Many thanks for answers to my first question to this list > yours > Alan >Hi, Alan, It might help if you print(x) in your integrate function. integrandtotest <- function(x) { print(x) a <- rep(0, len=2) for(i in 1:2) { a[i] <- tt[i]^x } sum(a) } integrate(integrandtotest, lower = 0.1, upper = 2) You will see that "x" is a vector and "tt[i]^x" returns a vector of the same length. You are trying to place this vector into "a[i]" which is length 1. Try the following *untested* code instead: <untested> integrandtotest <- function(x) { sum(sapply(x, function(xi) sum(tt^xi))) } integrate(integrandtotest, lower = 0.1, upper = 2) </untested> Also, I would avoid using "t" as a variable name. "t" is also a function. Most of the time R can tell the difference, but sometimes it cannot. HTH, --sundar
Try to give a vector result with one element for each of element of x, e.g. integrandtotest <- function(x) colSums(outer(t, x, "^")) works, although in fact this integration can be done analytically (it is a sum of exponentials). On Fri, 16 Sep 2005, A.Brennan wrote:> Hi > > i am having a problem with the 'integrate' function > the function i want to integrate has the form > sum(vector^x) > > i have defined the function with a for loop first - > integrandtotest <- function(x) > {a<-rep(0,len=2) > for (i in 1:2) > {a[i]<-t[i]^x} > sum(a) > } > > the results gives errors > ########### > Error in integrate(integrandtotest, lower = 0.1, upper = 2, > subdivisions = 10000) : > evaluation of function gave a result of wrong length > In addition: Warning messages: > 1: number of items to replace is not a multiple of replacement > length > 2: number of items to replace is not a multiple of replacement > length > ####### > > I then tried a vector multiplication instead of the for loop > > > integrandtotest3 <- function(x) > {b<-c(t[1],t[2]) > a<-b^x > sum(a) > } > > which gave errors > ######## > Error in integrate(integrandtotest3, lower = 0.1, upper = 2, > subdivisions = 10000) : > evaluation of function gave a result of wrong length > In addition: Warning message: > longer object length > is not a multiple of shorter object length in: b^x > ########## > > but when i write the functio out long-hand as follows: > > integrandtotest2 <- function(x) > {t[1]^x+t[2]^x} > > the integrate function works perfectly....... > ### >> integralresulttotest2<-integrate(integrandtotest2, lower=0.1, > upper=2, subdivisions=10000) >> integralresulttotest2 > 1.642369 with absolute error < 1.8e-14 > ### > > Unfortunatley my real life example has the vector a with length at > least 100. > > Is the any way round these errors? > > Many thanks for answers to my first question to this list > yours > Alan > > > > Alan Brennan > Director of Health Economics and Decision Science > http://www.shef.ac.uk/scharr/sections/heds > ScHARR > School of Health and Related Research > University of Sheffield > Regent Ct > 30 Regent St > Sheffield S1 4DA > Tel:+44 (0)114 2220684 > Fax:+44 (0)114 2724095 > e-mail:a.brennan at sheffield.ac.uk > > ______________________________________________ > R-help at stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html >-- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595
Thanks Sundar what you suggested worked fine> You will see that "x" is a vector and "tt[i]^x" returns a vector of the > same length. You are trying to place this vector into "a[i]" which is > length 1. Try the following *untested* code instead: > > <untested> > integrandtotest <- function(x) { > sum(sapply(x, function(xi) sum(tt^xi))) > }except you are summing twice so it should be......... integrandtotest <- function(x) {(sapply(x, function(xi) sum(tt^xi))) Alan Brennan Director of Health Economics and Decision Science http://www.shef.ac.uk/scharr/sections/heds ScHARR School of Health and Related Research University of Sheffield Regent Ct 30 Regent St Sheffield S1 4DA Tel:+44 (0)114 2220684 Fax:+44 (0)114 2724095 e-mail:a.brennan at sheffield.ac.uk
Thankyou Brian> integrandtotest <- function(x) colSums(outer(t, x, "^")) >This worked fine>in fact this integration can be done analytically (it is a > sum of exponentials).I know but i have another five terms in the integrand as well as the one that was causing the trouble Many, many thanks Alan