R: Solve a nonlinear equation system with multiple roots from...

searchZeros {nleqslv} | R Documentation

## Solve a nonlinear equation system with multiple roots from multiple initial estimates

### Description

This function solves a system of nonlinear equations with `nleqlsv` for multiple initial estimates of the roots.

### Usage

    searchZeros(x, fn, digits=4, ... )

### Arguments

`x` | A matrix with each row containing an initial guess of the roots.
`fn` | A function of `x` returning a vector of function values with the same length as the vector `x`.
`digits` | integer passed to `round` for locating and removing duplicate rounded solutions.
`...` | Further arguments to be passed to `nleqslv`, `fn` and `jac`.

### Details

Each row of `x` is a vector of initial estimates for the argument `x` of `nleqslv`. The function runs `nleqslv` for each row of the matrix `x`. The first initial value is treated separately and slightly differently from the other initial estimates. It is used to check if all arguments in `...` are valid arguments for `nleqslv` and the function to be solved. This is done by running `nleqslv` with no condition handling. If an error is then detected an error message is issued and the function stops. For the remaining initial estimates `nleqslv` is executed silently. Only solutions for which the `nleqslv` termination code `tcode` equals `1` are regarded as valid solutions. The rounded solutions (after removal of duplicates) are used to order the solutions in increasing order. These rounded solutions are not included in the return value of the function.

### Value

If no solutions are found `NULL` is returned. Otherwise a list containing the following components is returned

`x`

  a matrix with each row containing a unique solution (unrounded)

`xfnorm`

  a vector of the function criterion associated with each row of the solution matrix `x`.

`fnorm`

  a vector containing the function criterion for every converged result

`idxcvg`

  a vector containing the row indices of the matrix of initial estimates for which function value convergence was achieved

`idxxtol`

  a vector containing the row indices of the matrix of initial estimates for which x-value convergence was achieved

`idxnocvg`

  a vector containing the row indices of the matrix of initial estimates which lead to an `nleqslv` termination code > 2

`idxfatal`

  a vector containing the row indices of the matrix of initial estimates for which a fatal error occurred that made `nleqslv` stop

`xstart`

  a matrix of the initial estimates corresponding to the solution matrix

`cvgstart`

  a matrix of all initial estimates for which convergence was achieved

### Examples

    # Dennis Schnabel example 6.5.1 page 149 (two solutions)
    set.seed(123)
    dslnex <- function(x) {
        y <- numeric(2)
        y[1] <- x[1]^2 + x[2]^2 - 2
        y[2] <- exp(x[1]-1) + x[2]^3 - 2
        y
    }
    xstart <- matrix(runif(50, min=-2, max=2),ncol=2)
    ans <- searchZeros(xstart,dslnex, method="Broyden",global="dbldog")
    ans

    # more complicated example
    # R. Baker Kearfott, Some tests of Generalized Bisection,
    # ACM Transactions on Methematical Software, Vol. 13, No. 3, 1987, pp 197-220

    # A high-degree polynomial system (section 4.3 Problem 12)
    # There are 12 real roots (and 126 complex roots to this system!)

    hdp <- function(x) {
        f <- numeric(length(x))
        f[1] <- 5 * x[1]^9 - 6 * x[1]^5 * x[2]^2 + x[1] * x[2]^4 + 2 * x[1] * x[3]
        f[2] <- -2 * x[1]^6 * x[2] + 2 * x[1]^2 * x[2]^3 + 2 * x[2] * x[3]
        f[3] <- x[1]^2 + x[2]^2 - 0.265625
        f
    }

    N <- 40 # at least to find all 12 roots
    set.seed(123)
    xstart <- matrix(runif(3*N,min=-1,max=1), N, 3)  # N initial guesses, each of length 3
    ans <- searchZeros(xstart,hdp, method="Broyden",global="dbldog")
    ans$x

[Package nleqslv version 3.3.1 Index]