Meths: added Laplacian

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

zUtil_Maths/gtMathsLaplacian.m

+function dd = gtMathsLaplacian(x)
+% FUNCTION dd = gtMathsLaplacian(x)
+% Computes the divergence of an n-dimensional vector object.
+
+    dims = size(x);
+    num_dims = numel(dims);
+    dd = cell(num_dims, 1);
+    for ii_d = 1:num_dims
+        padsize = zeros(1, num_dims);
+        padsize(ii_d) = 1;
+
+        dd{ii_d} = diff(padarray(x, padsize, 'both'), 2, ii_d);
+    end
+
+    dd = gtMathsSumCellVolumes(dd);
+end
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