# Problem definition

An external C program is provided that compute the output of the Ishigami function:

$f(x_1,x_2,x_3) = \sin(x_1) + a \sin^2 (x_2) + b x_3^4 \sin(x_1)$

The Ishigami function of Ishigami & Homma (1990) is used as an example for uncertainty and sensitivity analysis methods, because it exhibits strong nonlinearity and nonmonotonicity. It also has a peculiar dependence on $x_3$.

## Input data

Parameter a = 7

Parameter b = 0.05

Function input $x_1$: uniform with lower bound $-\pi$, upper bound $\pi$.

Function input $x_2$: uniform with lower bound $-\pi$, upper bound $\pi$.

Function input $x_3$: uniform with lower bound $-\pi$, upper bound $\pi$.

# Aim of the Tutorial

The aim of the tutorial is to show how to connect a third party solver to COSSAN-X.

# Prerequisite

Compile the c file ishigamiFunction.c in OpenSourceSoftware/src/ishigamiFunction with the command:

Linux and MacOS X

gcc ishigamiFunction.c ini.c -lm -o ishigamiFunction

Windows (requires a gcc installation, e.g., tdm-gcc-64

gcc ishigamiFunction.c ini.c -lm -o ishigamiFunction.exe