MatchedSystemStructure: Print derivative/primal in separate columns

This makes it a bit easier to scan and follow derivative relationships:

```
 #   ∂ₜ         eq                  #   ∂ₜ          v
 1              ∅                |  1   7↑          [3, (5)]
 2              ∅                |  2   9↑          ∅
 3              [1, 5, (11)]     |  3   8↑          [4, (6)]
 4              [3, 5, (12)]     |  4   10↑         ∅
 5   7↑         [(1), 6]         |  5               [3, 4]
 6   8↑         [(3), 6]         |  6   13↑       ∫ [5, 6, 7, 8, 9, 10]
 7   9↑   5↓    [6, (7), 13]     |  7   11↑  1↓     [(7)]
 8   10↑  6↓    [6, (8), 13]     |  8   12↑  3↓     [(8)]
 9        7↓    [6, 11, 13, 14]  |  9        2↓     ∅
 10       8↓    [6, 12, 13, 14]  |  10       4↓     ∅
                ⋅                |  11       7↓     [(3), 9]
                ⋅                |  12       8↓     [(4), 10]
                ⋅                |  13  14↑  6↓   ∫ [7, 8, 9, 10]
                ⋅                |  14       13↓    [9, 10]
```

It also makes the diff more useful by showing when, e.g. the derivative
of variable `x` is still the same but a derivative of `x` has been newly
added to the system.

Author: topolarity

ext/MTKDeepDiffsExt.jl

@@ -1,9 +1,10 @@
 module MTKDeepDiffsExt
 
 using DeepDiffs, ModelingToolkit
-using ModelingToolkit.BipartiteGraphs: Label, BipartiteAdjacencyList, unassigned
+using ModelingToolkit.BipartiteGraphs: Label, BipartiteAdjacencyList, unassigned,
+                                       HighlightInt
 using ModelingToolkit.SystemStructures: SystemStructure, MatchedSystemStructure,
-                                        SystemStructurePrintMatrix, HighlightInt
+                                        SystemStructurePrintMatrix
 
 """
 A utility struct for displaying the difference between two HighlightInts.
@@ -162,7 +163,7 @@ end
 
 function Base.getindex(ssdpm::SystemStructureDiffPrintMatrix, i::Integer, j::Integer)
     checkbounds(ssdpm, i, j)
-    if i > 1 && (j == 3 || j == 7)
+    if i > 1 && (j == 4 || j == 9)
         old = new = BipartiteAdjacencyList(nothing, nothing, unassigned)
         (i <= size(ssdpm.new, 1)) && (new = ssdpm.new[i, j])
         (i <= size(ssdpm.old, 1)) && (old = ssdpm.old[i, j])

src/systems/systemstructure.jl

@@ -405,30 +405,31 @@ function SystemStructurePrintMatrix(s::SystemStructure)
                                       complete(s.eq_to_diff),
                                       nothing)
 end
-Base.size(bgpm::SystemStructurePrintMatrix) = (max(nsrcs(bgpm.bpg), ndsts(bgpm.bpg)) + 1, 7)
-function compute_diff_label(diff_graph, i)
+Base.size(bgpm::SystemStructurePrintMatrix) = (max(nsrcs(bgpm.bpg), ndsts(bgpm.bpg)) + 1, 9)
+function compute_diff_label(diff_graph, i, symbol)
     di = i - 1 <= length(diff_graph) ? diff_graph[i - 1] : nothing
-    ii = i - 1 <= length(invview(diff_graph)) ? invview(diff_graph)[i - 1] : nothing
-    return Label(string(di === nothing ? "" : string(di, '↑'),
-                        di !== nothing && ii !== nothing ? " " : "",
-                        ii === nothing ? "" : string(ii, '↓')))
+    return di === nothing ? Label("") : Label(string(di, symbol))
 end
 function Base.getindex(bgpm::SystemStructurePrintMatrix, i::Integer, j::Integer)
     checkbounds(bgpm, i, j)
     if i <= 1
-        return (Label.(("#", "∂ₜ", "  eq", "", "#", "∂ₜ", "  v")))[j]
-    elseif j == 4
+        return (Label.(("#", "∂ₜ", " ", "  eq", "", "#", "∂ₜ", " ", "  v")))[j]
+    elseif j == 5
         colors = Base.text_colors
         return Label("|", :light_black)
     elseif j == 2
-        return compute_diff_label(bgpm.eq_to_diff, i)
-    elseif j == 6
-        return compute_diff_label(bgpm.var_to_diff, i)
+        return compute_diff_label(bgpm.eq_to_diff, i, '↑')
+    elseif j == 3
+        return compute_diff_label(invview(bgpm.eq_to_diff), i, '↓')
+    elseif j == 7
+        return compute_diff_label(bgpm.var_to_diff, i, '↑')
+    elseif j == 8
+        return compute_diff_label(invview(bgpm.var_to_diff), i, '↓')
     elseif j == 1
         return Label((i - 1 <= length(bgpm.eq_to_diff)) ? string(i - 1) : "")
-    elseif j == 5
+    elseif j == 6
         return Label((i - 1 <= length(bgpm.var_to_diff)) ? string(i - 1) : "")
-    elseif j == 3
+    elseif j == 4
         return BipartiteAdjacencyList(i - 1 <= nsrcs(bgpm.bpg) ?
                                       𝑠neighbors(bgpm.bpg, i - 1) : nothing,
                                       bgpm.highlight_graph !== nothing &&
@@ -438,7 +439,7 @@ function Base.getindex(bgpm::SystemStructurePrintMatrix, i::Integer, j::Integer)
                                       bgpm.var_eq_matching !== nothing &&
                                       (i - 1 <= length(invview(bgpm.var_eq_matching))) ?
                                       invview(bgpm.var_eq_matching)[i - 1] : unassigned)
-    elseif j == 7
+    elseif j == 9
         match = unassigned
         if bgpm.var_eq_matching !== nothing && i - 1 <= length(bgpm.var_eq_matching)
             match = bgpm.var_eq_matching[i - 1]