Hello Taj Akbar. Using the REGRESSION command, you would have to compute new variables for the product terms in your model. E.g.,

COMPUTE Msq = M**2.

COMPUTE XM = X*M.

COMPUTE XMsq = X*M**2.

And then, you would simply include those new variables as explanatory variables in your model. But note that any model you can estimate using the REGRESSION command can also be estimated using the UNIANOVA (or equivalent GLM) command. The advantages of UNIANOVA are 1) that it allows you to distinguish between factor (or categorical) variables and metric (or quantitative) variables, and 2) it allows you to specify product terms on the DESIGN sub-command, with no need to compute new variables for the product terms. For the example you gave, the code would look something like this:

UNIANOVA Y WITH X M

/PRINT PARAMETER

/DESIGN= X M M*M X*M X*M*M

.

Give it a try. HTH.

PS- Note that this thread is a continuation of an earlier thread that Taj Akbar initiated. Here is the link to the original thread:

https://www.researchgate.net/post/How_to_run_a_non-linear_equation_in_SPSS

For this work, you can use the process macro (in SPSS) as well.