# How to enter equation while specifying terms?

Posted 3 months ago
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 Hello,I have tried to learn how to enter an equation and then rearrange it such that I can isolate each variable on one side of the equation. I need to specify instances in which certain terms are constant coefficients, and others where they are variables (functions).This is an example:H=BS+KE+AX+CT+J*F,where in the simplest case B, K, A, C and J are all constants and the rest are variables of independent functions.I would like to rearrange the equation to express it in terms of each variable (each of S, E, X, T and F isolated on the LHS), while specifying the constants listed above).Then, I want to specify a cases where one or all of the constant coefficients as originally specified are no longer constant, but variable.I am relatively inexperienced with Mathematica, more so for symbolic operations. However, I have read more pages from the Mathematica language documentation than I can keep track of, but nothing, so far, seems to address my goals.Eventually, I will want to derive expressions for the various partial derivatives for the expressions, but I need the expressions first.I will appreciate any assistance the community may provide, whether sending me to the relevant documentation or providing an exemplary input line. Best Regards,Paul Answer
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Posted 3 months ago
 There should be a multiplications sign between each of the first first four terms, and the fifth term which is correctly displayed.I am not sure why the other asterisks are not displayed. They are in my entry, but not in the post.Paul Answer
Posted 3 months ago
 Hi Paul,Symbol names that start with a capital letter are reserved for WL built-in symbols, so avoid them to prevent conflicts. ClearAll[h, b, s, k, e, a, x, c, t, j, f] eq = h == b*s + k*e + a*x + c*t + j*f Solve[eq, s] (* {{s -> (h - f j - e k - c t - a x)/b}} *) Solve[eq, f] (* {{f -> (h - e k - b s - c t - a x)/j}} *) Not sure what you mean by Then, I want to specify a cases where one or all of the constant coefficients as originally specified are no longer constant, but variable You can assign a value to a symbol and re-evaluate the expression. j = 3 Solve[eq, f] (* {{f -> 1/3 (h - e k - b s - c t - a x)}} *) Answer
Posted 3 months ago
 Thanks for the reminder on caps.As for constant coefficients: in simplest case, b, k, a, c and j are any real number, but constant, so that, for example, d(bs)/ds=b. The later case, where b is a function, say z=b*s and z'=b's+bs'.Again, not all * symbols post, for some reason.Thanks,Paul Answer
Posted 3 months ago
 not all * symbols post, for some reason Because * and ** have a special meaning (italics and bold) in Markdown. Read the "Post Editor" section here. Answer
Posted 3 months ago
 To further elaborate, consider the case for solving the equation for T. -ct=bs+ke+jf-h gives t=(1/c)h-(b/c)s-(k/c)e-(j/c)f. Furthermore, the initial h=... equation is an empirically-derived expression that relates the process variables, and empirically derived values are used for the values of the coefficients.I want to consider cases for which coefficient(s) are actually variables, and thus contribute to non-linear behavior of the linear relationship. Thanks,Paul Answer
Posted 3 months ago
 I think I've resolved this. There was no need to specify constant versus non-constant terms in the basic equations.It is handled when taking derivatives through use of NonConstants{terms}.Regards,Paul Answer