1: $f (n)$ – double array: $e^{- |x_{i}|} I_{0} (x_{i})$ , the function values.
2: $ifail$ – int64int32nag_int scalar: $ifail = 0$ unless the function detects an error (see Error Indicators and Warnings).

Error Indicators and Warnings

Errors or warnings detected by the function:

Cases prefixed with W are classified as warnings and do not generate an error of type NAG:error_n. See nag_issue_warnings.

W $ifail = 1$: Constraint: $n \geq 0$ .

$ifail = - 99$: An unexpected error has been triggered by this routine. Please contact NAG.

$ifail = - 399$: Your licence key may have expired or may not have been installed correctly.

$ifail = - 999$: Dynamic memory allocation failed.

Accuracy

Relative errors in the argument are attenuated when propagated into the function value. When the accuracy of the argument is essentially limited by the machine precision, the accuracy of the function value will be similarly limited by at most a small multiple of the machine precision.

Further Comments

None.

Example

This example reads values of x from a file, evaluates the function at each value of

x_{i}

and prints the results.

Open in the MATLAB editor: s18cs_example

function s18cs_example


fprintf('s18cs example results\n\n');

x = [0; 0.5; 1; 3; 6; 10; 1000; -1];

[f, ifail] = s18cs(x);

fprintf('     x        e^-|x| I_0(x)\n');
for i=1:numel(x)
  fprintf('%12.3e%12.3e\n', x(i), f(i));
end

s18cs example results

     x        e^-|x| I_0(x)
   0.000e+00   1.000e+00
   5.000e-01   6.450e-01
   1.000e+00   4.658e-01
   3.000e+00   2.430e-01
   6.000e+00   1.667e-01
   1.000e+01   1.278e-01
   1.000e+03   1.262e-02
  -1.000e+00   4.658e-01

PDF version (NAG web site, 64-bit version, 64-bit version)

Chapter Contents

Chapter Introduction

NAG Toolbox