make iterators doctest less expensive

Author: ranocha

docs/src/iterators.md

@@ -31,55 +31,44 @@ Now if you apply Jacobi iteration multiple times with the same matrix for just a
 ```jldoctest
 julia> using LinearAlgebra, SparseArrays, IterativeSolvers
 
-julia> A = sprand(10_000, 10_000, 10 / 10_000) + 20I;
+julia> A = spdiagm(-1 => -ones(3), 0 => 2*ones(4), 1 => -ones(3));
 
-julia> b1 = rand(10_000);
+julia> b1 = [1.0, 2, 3, 4];
 
-julia> b2 = rand(10_000);
+julia> b2 = [-1.0, 1, -1, 1];
 
-julia> x = rand(10_000);
+julia> x = [0.0, -1, 1, 0];
 
-julia> my_iterable = IterativeSolvers.jacobi_iterable(x, A, b1, maxiter = 4);
+julia> my_iterable = IterativeSolvers.jacobi_iterable(x, A, b1, maxiter = 2);
+
+julia> norm(b1 - A * x) / norm(b1)
+1.2909944487358056
 
 julia> for item in my_iterable
            println("Iteration for rhs 1")
        end
 Iteration for rhs 1
 Iteration for rhs 1
-Iteration for rhs 1
-Iteration for rhs 1
 
-julia> relative_residual = norm(b1 - A * x) / norm(b1);
+julia> norm(b1 - A * x) / norm(b1)
+0.8228507357554791
 
 julia> # Copy the next right-hand side into the iterable
        copyto!(my_iterable.b, b2);
 
+julia> norm(b2 - A * x) / norm(b2)
+2.6368778887161235
+
 julia> for item in my_iterable
            println("Iteration for rhs 2")
        end
 Iteration for rhs 2
 Iteration for rhs 2
-Iteration for rhs 2
-Iteration for rhs 2
 
-julia> relative_residual ≈ norm(b2 - A * x) / norm(b2)
-false
+julia> norm(b2 - A * x) / norm(b2)
+1.610815496107484
 ```
 
-This would output:
-
-```
-Iteration for rhs 1
-Iteration for rhs 1
-Iteration for rhs 1
-Iteration for rhs 1
-norm(b1 - A * x) / norm(b1) = 0.08388528015119746
-Iteration for rhs 2
-Iteration for rhs 2
-Iteration for rhs 2
-Iteration for rhs 2
-norm(b2 - A * x) / norm(b2) = 0.0003681972775644809
-```
 
 ## Other use cases
 Other use cases include: