genspmat2

gistfile1.jl

function genspmat2(N)
    iseven(N) && error("even N not allowed")
    
    # Determine memory usage
    k = N^2
    for i in 1:N^2
        if i > N
            k += 2
        elseif i > 1
            k += 1
        end
        if i <= (N-1)*N
            k += 2
        elseif i <= (N-1)*(N+1)
            k += 1
        end
    end

    # Preallocate
    I = Array(Int64,k)
    J = Array(Int64,k)
    V = Array(Int64,k)

    k = 0
    for i in 1:N^2
        m = getm(i,N)
        n = getn(i,N)
        k += 1
        J[k] = i; I[k] = i; V[k] = m*m+n*n
        if i > N
            k += 1
            J[k] = i-N; I[k] = i; V[k] = 1
            k += 1
            J[k] = i-1; I[k] = i; V[k] = m
        elseif i > 1
            k += 1
            J[k] = i-1; I[k] = i; V[k] = m
        end
        if i <= (N-1)*N
            k += 1
            J[k] = i+1; I[k] = i; V[k] = m
            k += 1
            J[k] = i+N; I[k] = i; V[k] = 1
        elseif i <= (N-1)*(N+1)
            k += 1
            J[k] = i+1; I[k] = i; V[k] = m
        end
    end
    return sparse(I,J,V)
end