Added examples for casting, made better examples for Maps

doc/AsciiQuickReference.txt

@@ -163,13 +163,25 @@ x.squaredNorm()           // dot(x, x)   Note the equivalence is not true for co
 x.dot(y)                  // dot(x, y)
 x.cross(y)                // cross(x, y) Requires #include <Eigen/Geometry>
 
+//// Type conversion
+// Eigen                           // Matlab
+A.cast<double>();                  // double(A)
+A.cast<float>();                   // single(A)
+A.cast<int>();                     // int32(A)
+// if the original type equals destination type, no work is done
+
+// Note that for most operations Eigen requires all operands to have the same type:
+MatrixXf F = MatrixXf::Zero(3,3);
+A += F;                // illegal in Eigen. In Matlab A = A+F is allowed
+A += F.cast<double>(); // F converted to double and then added (generally, conversion happens on-the-fly)
+
 // Eigen can map existing memory into Eigen matrices.
 float array[3];
-Map<Vector3f>(array, 3).fill(10);
-int data[4] = 1, 2, 3, 4;
-Matrix2i mat2x2(data);
-MatrixXi mat2x2 = Map<Matrix2i>(data);
-MatrixXi mat2x2 = Map<MatrixXi>(data, 2, 2);
+Vector3f::Map(array).fill(10);            // create a temporary Map over array and sets entries to 10
+int data[4] = {1, 2, 3, 4};
+Matrix2i mat2x2(data);                    // copies data into mat2x2
+Matrix2i::Map(data) = 2*mat2x2;           // overwrite elements of data with 2*mat2x2
+MatrixXi::Map(data, 2, 2) += mat2x2;      // adds mat2x2 to elements of data (alternative syntax if size is not know at compile time)
 
 // Solve Ax = b. Result stored in x. Matlab: x = A \ b.
 x = A.ldlt().solve(b));  // A sym. p.s.d.    #include <Eigen/Cholesky>