The fit utility will generate, compile, link, and execute a
FORTRAN program to fit a set of data points to a user-provided equation
using the SIMPLEX algorithm. The data points and initial guesses for the
adjustable parameters will be read from a file. The equation for the
function has to be provided when prompted as a single, correct FORTRAN
statement evaluating a variable called YCALC, e.g. :
YCALC = A(1) + A(2)*X(1) + A(3)*X(2)
where the A(i)'s represent the parameters to be determined, and the X(i)'s
the independent variables. The equation can be non-linear in either the
parameters or the variables. Both the variables and the parameters have
to be given in the same sequence that they appear in the input file, and
the indeces have to be continuously increasing, unless refering to a
previously defined variable or parameter, i.e. :
the equation YCALC=A(1)+A(2)*X(1)+A(4)*X(2) is NOT valid since the
sequence of A's is broken.
the sequence YCALC=A(1)+A(2)*X(1)+(A(1)+A(2))*X(2) is valid.
the input equation is terminated by a , thus a single line must be
used. This line can however be up to 256 characters long and wraps around
when the edge of the screen is reached. The equation is parsed, converted
to lower case, and broken into all the necessary FORTRAN lines by this
utility.
The input file should contain in the first line the initial guesses for
the values of all the parameters in the sequence established by the
indeces assigned in the equation. The remaining lines should contain the
values for all the variables in the sequence of their assignement,
followed by the "observed" value of the dependent variable (Y). All these
values are read in free format and the program will recognize normal real,
exponential, or integer numbers as input. The only requirements are that
all the values for the independent and dependent variables are given in
the same line for each point, and that they are separated by at least one
blank. Alphanumeric text or comments can be present and the program will
ignore them.
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