diff2_center, an Octave code which interactively uses centered differences to estimate the second derivative of a function f(x), using a stepsize h.
If a call is made of the form
yp = diff2_center ( f_string, x, h );
then x can be a vector. Otherwise, x should be a single value.
The program returns yp, the centered difference estimate for f"(x).
The program can be invoked by a function call, in which case the string specifying f(x) must be quoted:
yp = diff2_center ( 'x^2', 1.0, 0.01 )
or, if called with no arguments, it will request them:
yp = diff2_center ( );
Enter function formula, like x^2: x^2
Enter evaluation point, x: 1.0
Enter stepsize, h: 0.01
The function is specified as a string which is either:
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 MIT license
diff2_center is available in a MATLAB version and an Octave version.
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