I am re-posting. I am not sure why my question was deleted. Please advise on how to amend my post so that it's not considered spam.

I simply wonder how parameters can "disappear" in a solution. In particular, in my example below the parameter gamma correctly appears in 3 out of 4 solution. However, the solution in which 'gamma' does not appear is also the solution I am most interested in, given its manageable size. Why gamma is "lost" for this solution? 281223_gamma_disappear.mw

I am solving 3 nonlinear equations for 3 variables: lambda_1, lambda_2, and lambda_3. I would expect these lambdas to be real and positive.

Instead of solving my original equations, which are convoluted and not in polynomial form, I try to solve for their numerators first (since their numerators are polynomials). Broadly speaking, such solutions should also solve the original non-polynomial system. More specifically, the solutions thus obtained may be a nontrivial superset of the solutions of the original system. They need to be verified, which should be a much much easier process than obtaining that superset. In the case at hand, my original system is rational functions, and thus the only thing that really needs to be verified is that the solutions do not make any of the original denominators zero.

1st question: How to actually implement such verification? In other words, how to verify that the polynomial solution that I obtain also solves the original non-polynomial system?

2nd question: As you can see from my attached script, I obtain one polynomial solution. How to analyze it? What can I say about its roots? In case there are an infinite number of roots, how can I pin down a closed-form, real, and positive expression of lambda_1, lambda_2, lambda_3 in terms of the four parameters gamma, p, sigma_e and sigma_v?*

*Please note that in SolveTools:-PolynomialSystem I set backsubstitute=false to favour compactness and computational efficiency (which means that I need to do the backsubstitution myself now - how to do it?).

**Perhaps is useful to know that gamma, sigma_e and sigma_v are all real and positive and that p is a real, positive number between 0 and 1 (it represents a probability).

SCRIPT: 141123_Problem_NoCorrelation.mw

Thanks a lot!

I have a linear system of 3 equations in 3 variables and have no issues with solving it using solve().

I am having issues with solving it by imposing assumptions on my parameters. The infolevel[solve] now outputs "Entering solver with 6 equations in 3 variables", so I am likely making mistakes in the syntax solve(Eqs, Vars, UseAssumptions) assuming ... first of all, do I even need to do this given the assume statements that I set up on top of my script? How do I make sure that all the assumptions are preserved throughout all the calculations in my worksheet?

Moreover, I don't know why I get SolutionsLost: setting solutions lost flag.

My script: 061123_solving_with_assumptions.mw

I have a system of 3 (very large) nonlinear equations in 3 variables. Since I cannot feed non-algebraic expressions into polynomial solvers, I want to extract only their numerators (which should be algebraic) and solve the three numerators for the 3 variables. These solutions should also solve the non-algebraic system then. 

This is the original system (sorry I don't know why but I was not able to include the massive expression in the startup code): System.mw

I think I am not understanding the syntax. To extract the numerators, I am using ((numer@evala@:-Norm@numer)~@eval)(Eqs) (scroll down to the very bottom of my script):

1. Am I wrong?
2. What exactly am I doing with this combined command?
3. Why length(((numer@evala@:-Norm@numer)~@eval)(Eqs)) is much larger than length(Eqs)? Shouldn't it be smaller since I just extract the numerators?

Thank you.

I am using this command: plotsetup(png, plotoutput = "titleofmylistofplots", plotoptions = "width=1920,height=1080")

in the execution block right before a sequence of split execution blocks, each made of plots:-display( seq( plot( [$ 20], series1of8[1..20,j], color=cols1[j]), j=1..3)); (I have 8 series: series1of8, series2of8, series3of8 and so on...)

When I open the output .png file, it only contains the last plot, that is the plot of series8of8. I want my file to contain all 8 plots. How to change the plotsetup() command accordingly?