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# XPRSslpchgcoefstr

Purpose
Add or change a single matrix coefficient using a character string for the formula. For a simpler version of this function see XPRSnlpchgformulastr.
Topic areas
SLP, Problem Modification
Synopsis
`int XPRS_CC XPRSslpchgcoefstr(XPRSprob prob, int row, int col, const double *factor, const char *formula);`
Arguments

prob | The current problem.
row | The index of the matrix row for the coefficient.
col | The index of the matrix column for the coefficient.
factor | Address of a double precision variable holding the constant multiplier for the formula. If factor is NULL, a value of 1.0 will be used.
formula | Character string holding the formula with the tokens separated by spaces.

Example
Assuming that the columns of the matrix are named Col1, Col2, etc, the following example puts the formula 2.5*sin(Col1) into the coefficient in row 1, column 3.

    char *formula="sin ( Col1 )";
    double factor;

    factor = 2.5;
    XPRSslpchgcoefstr(prob, 1, 3, &factor, formula);

Note that all the tokens in the formula (including mathematical operators and separators) are separated by one or more spaces.
Further information
1. If the coefficient already exists as a constant or formula, it will be changed into the new coefficient. If it does not exist, it will be added to the problem.
2. A coefficient is made up of two parts: factor and formula. factor is a constant multiplier which can be provided in the factor variable. If Xpress NonLinear can identify a constant factor in the formula, then it will use that as well, to minimize the size of the formula which has to be calculated.
3. This function can only be used if all the operands in the formula can be correctly identified as constants, existing columns, character variables or functions. Therefore, if a formula refers to a new column, that new item must be added to the Xpress NonLinear problem first.
Related topics
XPRSnlpgetformulastr, XSLPaddformulas, XPRSnlpchgformulastr, XSLPchgformula, XSLPloadformulas, XSLPgetformularows, XSLPgetformula, XSLPdelformulas
Parent Topic Library functions and the programming interface

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