**nonlin_regula**,
a MATLAB code which
interactively applies the regula falsi method to seek a root of f(x)
over a change-of-sign interval a <= x <= b.

The user enters a formula for f(x), and the values of a and b. It must be the case that the signs of f(a) and f(b) are opposite.

The program then repeatedly applies the regula falsi method until the width of the interval is very small.

The program can be invoked by a function call, in which case the string specifying f(x) must be quoted:

[ a, b, fa, fb ] = nonlin_regula ( 'x^2-4', -1, 3 )or, if called with no arguments, it will request them:

[ a, b, fa, fb ] = nonlin_regula ( ); Enter function formula, like x^2-4: x^2-4 Enter left limit, a: -1 Enter right limit, b: 3

The function is specified as a string which is either:

- a MATLAB expression using the argument 'x';
- the name of an M-file followed by the argument '(x)'.

The string should not contain any spaces between symbols, except when it is passed as a function argument in quotes.

It is not necessary to use the "dot" notation for expressions involving '*', '/', or '^', but it doesn't hurt either.

Examples of function specifications:

x^2 x.^2 3/(x^4+5*x-6) sin(7*x)*sqrt(x)/8 wiggle(x) <-- where "wiggle.m" is a user-provided M file.

The computer code and data files made available on this web page are distributed under the GNU LGPL license.

**nonlin_regula** is available in
a MATLAB version.

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- nonlin_regula.m the source code.