# Re: [R] Package nleqslv ERROR

```Maybe it's simpler to point out that nonlinear EQUATIONS need n equations for n
unknowns.```
```
4 only equals 2 through the looking glass.

Alternatively, maybe the OP wants to adjust the 2 parameters to best fit the 4
relationships, in which
case nlsr package function nlfb() would be appropriate. Note that nls() in base
R tends to not like
small residual problems and tends to give other warnings and errors.

JN

On 2017-08-09 05:32 PM, Mark Sharp wrote:
```
```Santi,

In the second line of your function you have the following:
f <- numeric(length(x))

This sets the length of this numeric vector (i.e., "f") to the length of the vector
"x".
Later, inside the function you assign to values to 4 elements of the vector "f".
This assumes that "f" is at least 4 element in length.

However, you define "startx" to be a numeric vector of length 2 with
startx <- c(16350, 1.33)
which you then use as the argument to the function "fun" (bad name for a
function, by the way, as it is not descriptive).

Thus, when "x" inside your function gets the value of "startx" it becomes a numeric
vector of length 2, which is then used to set the length of the numeric vector "f". As soon as the
function tries to assign a value to f[3], R correctly throws an informative error.

Mark
R. Mark Sharp, Ph.D.
msh...@txbiomed.org

```
```On Aug 9, 2017, at 3:56 PM, Santi Burone <santiagobur...@gmail.com> wrote:

Dear all,
I am relatively new to R and have had some difficulty in understanding an error
i get when running a code to solve a system of non-linear equations, with four
equations and two variables.

This is my code:

ALPHA <- c(-0.0985168033402, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4)
BETA <- c(-0.0985168033402, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4)
GAMMA <- c(0.3940672148378, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4)
MEA <- 30000
MIA <- 10000
MAA <- 50000
DEA <- 0.385
fun <- function(x)  {
f <- numeric(length(x))
f[1] <-   1*x[1] -
((((MEA*((0.5*((MIA-MEA)^2))^(-BETA[1+j]))*((0.5*((MAA-MEA)^2))^(-ALPHA[1+i]))*((DEA)^(-GAMMA[1+k]))))*((12^0.5)^(-GAMMA[1+k])))/(((0.5)^(-BETA[1+j]-ALPHA[1+i]))*(((1-1*x[2])/(2))^(-BETA[1+j]))*(((-1+1*x[2])/(2))^(-ALPHA[1+i]))*(2*(1*x[2]-1)^(-GAMMA[1+k]))))^(1/(-1-BETA[1+j]-ALPHA[1+i]-1.5*GAMMA[1+k]))
f[2] <-   1*x[1] -
(((MAA*((0.5*((MIA+MAA)^(2)))^(-BETA[1+j]))*((DEA)^(-GAMMA[1+k])))*((12^0.5)^(-GAMMA[1+k])))/((1*x[2])*(2^(-BETA[1+j]-GAMMA[1+k]))*((1*x[2]-1)^(-GAMMA[1+k]))*((((1-1*x[2])^2)/2)^(-BETA[1+j]))))^(1/(1-2*BETA[1+j]-1.5*(GAMMA[1+k])))
f[3] <-   1*x[1] -
(((MIA*((0.5*((MIA+MAA)^(2)))^(-ALPHA[1+i]))*((DEA)^(-GAMMA[1+k])))*((12^0.5)^(-GAMMA[1+k])))/((2-1*x[2])*(2^(-ALPHA[1+i]-GAMMA[1+k]))*((1*x[2]-1)^(-GAMMA[1+k]))*((((-1+1*x[2])^2)/2)^(-ALPHA[1+i]))))^(1/(1-2*ALPHA[1+i]-1.5*(GAMMA[1+k])))
f[4] <- 1*x[2] > 1
f

}

Result <- matrix(0,nrow=9*9*9,ncol=6)
startx<-c(16350, 1.33)
indx <- 1
for (i in 1:9) {
for (j in 1:9) {
for (k in 1:9) {
f.startx <- fun(startx)
if(anyNA(f.startx)) {
Result[indx,1:3] <- NA
} else {
z <- nleqslv(startx,fun)
Result[indx,1:3] <- c(z\$termcd,z\$x)
}
Result[indx,4:6] <- c(i,j,k)
indx <- indx+1
}
}
}

The error i get when solving for specific values of ALPHA, BETA and GAMMA, not
using the loop is:

Error in nleqslv(xstart, fun) : Length of fn result <> length of x!

I had already solved this problem useing ALPHA, BETA and GAMMA as X[1], X[2]
and X[3] and being X[1] and X[2] of this system  given values, in that case for
the first values of alpha beta and gamma given here the solution was (16350,
1.33).
I dont understand what’s the error i get here, as i know the system as a unique solution.
"What’s the meaning of Length of fn result <> length of x!"?

Santiago.
[[alternative HTML version deleted]]

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