added MERG example using iterative diagonalisation

examples/KondoMERG.jl

@@ -0,0 +1,48 @@
+using fermions
+
+function RGFlow(
+        energies::Vector{Float64},
+        kondoJ::Float64,
+        dofStates::Function,
+    )
+    @assert length(energies) > 1
+    @assert issorted(energies, rev=true)
+    kondoJFlow = [kondoJ]
+    for (i, energy) in enumerate(energies)
+        if energy - kondoJFlow[end]/4 < 0
+            return kondoJFlow, i-1
+        end
+        if kondoJFlow[end] < 0
+            kondoJFlow[end] = 0
+            return kondoJFlow, i-1
+        end
+        deltaEnergy = i < length(energies) ? energies[i] - energies[i+1] : energies[i-1] - energies[i]
+        deltaKondoJ = dofStates(energy, maximum(energies)) * kondoJFlow[end]^2 * deltaEnergy / (energy - kondoJFlow[end]/4)
+        push!(kondoJFlow, deltaKondoJ + kondoJFlow[end])
+    end
+    return kondoJFlow, length(energies)
+end
+
+D = 3.
+deltaD = 0.01
+kondoJ = 0.2 * D
+dofStates = (E,D) -> (1/D)*(1 - E^2/D^2)^0.5
+energies = collect(D:-deltaD:0)
+kondoJFlow, fixedPointStep = RGFlow(energies, kondoJ, dofStates)
+
+totalSites = 11
+initStates = 5
+kondoJMatrix = zeros(totalSites, totalSites)
+kondoJMatrix[1:initStates,1:initStates] .= kondoJFlow[end]
+for i in 1:(totalSites - initStates)
+    kondoJMatrix[initStates+i, 1:initStates+i] .= kondoJFlow[end - i]
+    kondoJMatrix[1:initStates+i, initStates+i] .= kondoJFlow[end - i]
+end
+hamltonian = KondoModel(energies[end:-1:end-totalSites+1], kondoJMatrix)
+hamiltonianFlow = MinceHamiltonian(hamltonian, collect(2 + 2 * initStates:4:2 + 2 * totalSites))
+savePaths, resultsDict = IterDiag(hamiltonianFlow, 500;
+                     symmetries=Char['N', 'S'],
+                     correlationDefDict=Dict("SF-d0" => [("+-+-", [1,2,4,3], 1.), ("+-+-", [2,1,3,4], 1.)]),
+                     calculateThroughout=true,
+                    ) 
+display(resultsDict)