Example

Author: tobiasgrosser

README.md

@@ -1 +1,58 @@
-# How to use isl via the C++ / Python interface
+Warning: This is a proposal, which does not document the current isl 
+
+# How to use isl via the C++ and Python interface
+
+## Constructing an integer set or map (isl::set / isl::map)
+
+We create an integer set as follows. We first create a set of identifiers for
+each of the needed dimensions (`isl::id Id_N(ctx, "N"`). We then introduce
+initial expressions for all identifiers and required constants (`isl::pw_aff
+N(Id_N), Ten(ctx, 10)`). From these initial expressions the actual affine
+expressions are constructed (`isl::pw_aff LHS = Two.mul(M)`). Pairs of
+expressions are combined with the operators lt_set (<), le_set (<=), ge_set
+(>=), gt_set (>), eq_set (=), ne_set (!=) into a parameteric set of constraints
+(`isl::set PSet = LHS.le_set(RHS)`). Finally, a non-parameteric set is
+constructed from 1) a parameteric set specifying its constraints and 2) a list
+of identifiers that specify the parameter dimensions that should be promoted to
+set dimensions (`isl::set Set({Id_i, Id_j}, PSet)`).  Similary, a map can be
+constructed by providing two lists of identifiers defining the input and output
+dimensions (`isl::map Map({Id_i}, {Id_j}, PSet)`)
+
+Example:
+*{ [N, M] -> { [i,j] : 2 * M + 3 * N <= 2 * i + j + 10 }*
+
+
+```
+// Identifiers
+isl::id Id_N(ctx, "N"), Id_M(ctx, "M"), Id_i(ctx, "i"), Id_j(ctx, "j");
+
+// One (piece-wise) affine expression per identifier
+isl::pw_aff N(Id_N), M(Id_M), i(Id_i), j(Id_j);
+
+// One (piece-wise) affine expression per constant
+isl::pw_aff Ten(ctx, 10), Two(ctx, 2), Three(ctx, 3);
+
+// Build the left and right hand side of the expression
+isl::pw_aff LHS = Two.mul(M).add(Three.mul(N));
+isl::pw_aff RHS = Two.mul(i).add(j).add(Ten);
+
+// [N, M, i, j] -> { : 2 * M + 3 * N <= 2 * i + j + 10 }
+isl::set PSet = LHS.le_set(RHS);
+
+// [N, M] -> { [i, j] : 2 * M + 3 * N <= 2 * i + j + 10 }
+isl::set Set({Id_i, Id_j}, PSet);
+
+// [N, M] -> { [i] -> [j] : 2 * M + 3 * N <= 2 * i + j + 10 }
+isl::map Map({Id_i}, {Id_j}, PSet);
+```
+
+- Comments
+
+  - Why do we need to create identifiers twice? Can we just do?
+
+```
+// One (piece-wise) affine expression per identifier
+isl::pw_aff N(ctx, "N"), M(ctx, "M"), i(ctx, i"), j(ctx, "j");
+```
+  This likely won't work as there is no way to obtain ids for the identifiers.
+