--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/+blockmatrix/isBlockmatrix.m	Fri Sep 07 14:40:58 2018 +0200
@@ -0,0 +1,59 @@
+function b = isBlockmatrix(bm)
+    if ~iscell(bm)
+        b = false;
+        return
+    end
+
+    % Make sure all blocks are numerical matrices
+    for i = 1:length(bm)
+        if ~isnumeric(bm{i})
+            b = false;
+            return
+        end
+    end
+
+    [N,M] = size(bm);
+    % Make sure column dimensions agree
+    for i = 1:N
+        d = [];
+        for j = 1:M
+            d_ij = size(bm{i,j},1);
+            if d_ij == 0
+                continue
+            end
+
+            if isempty(d)
+                d = d_ij;
+                continue
+            end
+
+            if d ~= d_ij
+                b = false;
+                return
+            end
+        end
+    end
+
+    % Make sure row dimensions agree
+    for j = 1:M
+        d = [];
+        for i = 1:N
+            d_ij = size(bm{i,j},2);
+            if d_ij == 0
+                continue
+            end
+
+            if isempty(d)
+                d = d_ij;
+                continue
+            end
+
+            if d ~= d_ij
+                b = false;
+                return
+            end
+        end
+    end
+
+    b = true;
+end