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For instance "X1 + X2 * 3". The following operators can be used in the expression: +, -, /, *, ^, sin, cos, tan, asin, acos, atan, sinh, cosh, tanh, asinh, acosh, atanh, log, ln, exp, sqrt, abs, pow.
In the expression reference input variables or coefficients using their id, e.g. "X1 + a" where "X1" is the variableId of a variable defined elsewhere and "a" is the id of a coefficient defined in a coefficientSet. A variableId or coefficientId should not start with a numerical character and should not contain operators. The following operators can be used in the expression: +, -, /, *, ^, sin, cos, tan, asin, acos, atan, sinh, cosh, tanh, asinh, acosh, atanh, log, ln, exp, sqrt, abs, pow. "pi" in lowercase letters is recognised as a standard constant. This means that the user cannot use variables or coefficients with id "pi".
Coefficient set
Should contain the coefficients that are used in the free format expression. Defined the ids and values of the coefficients here, then reference to the ids of these coefficients in the expression. Make sure that for all the coefficient ids in the free format expression the values are defined here.
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