There are syntax errors in your PDE. Would you please try uploading it again? Or upload a worksheet.

@Bendesarts I tried the links in Markiyan's Reply and yours and I just get "Error 404---File not found". I've tried in three web browsers: Internet Explorer, Firefox, and Pale Moon. This may be related to the recent MaplePrimes software update.

The link in your Question does not work. It is asking for login credentials. Please upload a Maple worksheet instead.

@bunmipopoola Preben did respond, but you didn't see it because of a bug in MaplePrimes. Because of the recent software update to MaplePrimes, you may need to refresh the webpage to see responses. In Internet Explorer, I need to refresh every page every time I visit it.

@Kitonum This model seems rather unlikely to me. The data are nondecreasing, but the model has a local maximum at x=1.83---just to the right of the end of the dataset. The marginal improvement in the fit that you get from the extra term (as measured by the first value returned by DataFit) seems too small to justify using the extra term.

@Adri van der Meer That should be

plot([X(t), Z(X(t)), t=0..10], numpoints= 200, color= blue, legend= "z(x)");

A problem is that some of your first coordinates are repeated. Can you get another digit of accuracy so that that is not the case?

It is not really working in IE either, but it's working better than in Firefox.

It's not really working in IE either, but it's working better than in Firefox.

@NoThik Only the first vector returned by IntegerLinearSolve satisfies the equation A.X=B. The remaining vectors are a basis for the nullspace of A.

@NoThik Only the first vector returned by IntegerLinearSolve satisfies the equation A.X=B. The remaining vectors are a basis for the nullspace of A.

@Alexander zhang I'm still thinking about it. I need to refresh my knowledge of surface integrals.

I can't view your image. Please upload a worksheet, not an image.

The diff_table is symmetric, so it won't let you control the order of the derivatives: F[x,y] is identical to F[y,x]. Look closely at the order that it places the derivatives:

lprint(F[x,y]);
diff(diff(f(x, y, w, z, a, b), x), y)
lprint(F[x,b]);
diff(diff(f(x, y, w, z, a, b), b), x)

In the first case the F[x] is an integral part of the expression, and hence it can be substituted. In the second case it is not an integral part of the expression, and hence it cannnot be substituted.

@Bendesarts Here are my results. Download the attached worksheet and run it on your system.

Download gamma.mw