@Scot Gould There are two problems with your derivative: 

• The symbolic derivative is recomputed for every invocation of drdt, including all the numeric points of the plot (if plotted in functional form).
• If global t is assigned a non-name value, the derivative won't work. 

@Carl Love Addendum: Using blocks= [u,v] should also work. It gives a different ranking of the derivatives. I think that the fact that it doesn't work should be considered a bug. Here is what the help page ?DifferentialRing says about the different rankings:

• Together, the lists blocks and derivations provide the ranking of R, that is, an ordering for the derivatives of the dependent variables with respect to the independent variables. In brief, the elements in blocks (dependent variables or sublists of them) are ranked between each other using an elimination ranking and those within a sublist are ranked used an orderly ranking.
  An elimination ranking is one where derivatives of leftmost dependent variables, or of all the dependent variables in a leftmost sublist within blocks, rank higher than derivatives of variables to their right. An orderly ranking is one where derivatives of higher differential order rank higher than derivatives of lower differential order, and if the order is the same, then derivatives of leftmost variables rank higher.

The precise bug that you encountered comes from a construction of the form a^b^c, which is always an error in Maple because it doesn't disambiguate between (a^b)^c and a^(b^c).

@janhardo By symmetry, the case A <> 0 and B=0 is equivalent to A=0 and B <> 0 with the roles of x and y switched. So, this case can be handled in your code by ans:= conics(0, A, D, C, E).

@nm Assumptions of equations specifying a value for a variable such as lambda=1 never work.

@emendes Just remove the one line that I specified. I don't think any other changes are needed.

Note that arg1 is not an argument to mainproc.

@janhardo The formula that you've used is sufficient for conics whose axes are parallel to the coordinate axes. For other conics, you need a term with both x and y. Conics include the degenerate cases of intersecting lines and a single point.

@imparter I said to switch them, not to replace Re with seq:

plot([seq(Re(eval(U1,tb=j)),j in[0.8,0.9,1.0])],r=0..1,legend = [tb =0.8, tb=0.9,tb =1.0],  labels = ["z ", "U"], labeldirections = ["horizontal", "vertical"],  linestyle = [solid,dash,dot],color = [black, red,green]);

@vs140580 There are three problems with your Reply:

• It's fairly far from the original Question.
• You never said whether the Answer provided a satisfactory solution to your original Question.
• You didn't apply the Answer to the graphs that you show in the Reply.

@janhardo Tom's op([2,1,2], A) means the same thing as op(2, op(1, op(2, A))). However, it is confusing to use this with an Array such as A because the op numbers depend on the internal structure rather than on features that are usually externally visible to the user.

@Preben Alsholm Another option is map[evalhf](sin, V). I don't know how this differs from evalhf(map(sin, V)).

From your writing, it seems that you have some Maple code that you want to modify. Please post that code.

@vv You need to reinitialize Pab in ModuleApply. If you don't, then your code will only work on its first run.

@janhardo Your problem is that a white surface is still opaque. Try this: Change the command defining the grid to

rooster:= plot3d(
      0, x= 0..2, y= 0..2, grid= [3,3], style= wireframe, 
      color= COLOR(RGB, .15$3), thickness= 0
)

The color option in my command specifies the color of the gridlines. The spaces in between are transparent and uncolored.

I think in another Question you said that you're using Maple 13. Is that correct? I don't know if Maple 13 has events. Is there a help page for it?

@Axel Vogt Perhaps. But it's well known and documented that (1) remember tables don't work with mutable containers, and (2) more importantly, that sum shouldn't be used with indexable structures. At ?sum, we read

• [I]t is strongly recommended that the add command be used in programs if an explicit sum is needed, in particular, when summing over all elements of a list, Array, Matrix, or similar data structure.