Tutorial page 3: add more cwise operations, condense rest.

doc/C03_TutorialArrayClass.dox

@@ -7,7 +7,7 @@ namespace Eigen {
 \li \b Next: \ref TutorialBlockOperations
 
 This tutorial aims to provide an overview and explanations on how to use
-Eigen's \link ArrayBase Array \endlink class
+Eigen's Array class.
 
 \b Table \b of \b contents
   - \ref TutorialArrayClassIntro
@@ -15,6 +15,7 @@ Eigen's \link ArrayBase Array \endlink class
   - \ref TutorialArrayClassAccess
   - \ref TutorialArrayClassAddSub
   - \ref TutorialArrayClassMult
+  - \ref TutorialArrayClassCwiseOther
   - \ref TutorialArrayClassConvert
 
 \section TutorialArrayClassIntro What is the Array class?
@@ -27,17 +28,17 @@ such as adding a constant to every coefficient in the array or multiplying two a
 
 \section TutorialArrayClassTypes Array types
 Array is a class template taking the same template parameters as Matrix.
-As with Matrix, the first 3 template parameters are mandatory:
+As with Matrix, the first three template parameters are mandatory:
 \code
 Array<typename Scalar, int RowsAtCompileTime, int ColsAtCompileTime>
 \endcode
-And the last 3 template parameters are optional. Since this is exactly the same as for Matrix,
+The last three template parameters are optional. Since this is exactly the same as for Matrix,
-we won't reexplain it and just refer to \ref TutorialMatrixClass "this page".
+we won't explain it again here and just refer to \ref TutorialMatrixClass.
 
 Eigen also provides typedefs for some common cases, in a way that is similar to the Matrix typedefs
 but with some slight differences, as the word "array" is used for both 1-dimensional and 2-dimensional arrays.
 We adopt that convention that typedefs of the form ArrayNt stand for 1-dimensional arrays, where N and t are
-as in the Matrix typedefs explained on \ref TutorialMatrixClass "this page". For 2-dimensional arrays, we
+the size and the scalar type, as in the Matrix typedefs explained on \ref TutorialMatrixClass "this page". For 2-dimensional arrays, we
 use typedefs of the form ArrayNNt. Some examples are shown in the following table:
 
 <table class="tutorial_code" align="center">
@@ -71,69 +72,103 @@ use typedefs of the form ArrayNNt. Some examples are shown in the following tabl
 
 
 \section TutorialArrayClassAccess Accessing values inside an Array
-Write and read access to coefficients of an array expression is done in the same way as with matrix expressions.
-For example:
 
-\include Tutorial_ArrayClass_accessors.cpp
+The parenthesis operator is overloaded to provide write and read access to the coefficients of an array, just as with matrices.
-Output:
+Furthermore, the \c << operator can be used to initialize arrays (via the comma initializer) or to print them.
-\verbinclude Tutorial_ArrayClass_accessors.out
 
-For more information about the comma initializer, refer to \ref TutorialAdvancedInitialization "this page".
+<table class="tutorial_code"><tr><td>
+Example: \include Tutorial_ArrayClass_accessors.cpp
+</td>
+<td>
+Output: \verbinclude Tutorial_ArrayClass_accessors.out
+</td></tr></table>
+
+For more information about the comma initializer, see \ref TutorialAdvancedInitialization.
 
 
-\section TutorialArrayClassAddSub Addition and substraction
+\section TutorialArrayClassAddSub Addition and subtraction
+
+Adding and subtracting two arrays is the same as for matrices.
+The operation is valid if both arrays have the same size, and the addition or subtraction is done coefficient-wise.
+
+Arrays also support expressions of the form <tt>array + scalar</tt> which add a scalar to each coefficient in the array.
+This provides a functionality that is not directly available for Matrix objects.
+
+<table class="tutorial_code"><tr><td>
+Example: \include Tutorial_ArrayClass_addition.cpp
+</td>
+<td>
+Output: \verbinclude Tutorial_ArrayClass_addition.out
+</td></tr></table>
 
 
-Adding and substracting two arrays has the same result as for Matrices.
+\section TutorialArrayClassMult Array multiplication
-This is valid as long as both arrays have the same sizes:
-
-\include Tutorial_ArrayClass_addition.cpp
-Output:
-\verbinclude Tutorial_ArrayClass_addition.out
-
-It is also allowed to add a scalar to each coefficient in an Array,
-providing a functionality that was not available for Matrix objects:
-
-\include Tutorial_ArrayClass_addition_scalar.cpp
-Output:
-\verbinclude Tutorial_ArrayClass_addition_scalar.out
-
-
-\subsection TutorialArrayClassMult Array multiplication
 
 First of all, of course you can multiply an array by a scalar, this works in the same way as matrices. Where arrays
-are fundamentally different from matrices, is when you multiply two arrays together. While Matrices interprete
+are fundamentally different from matrices, is when you multiply two together. Matrices interpret
-multiplication as matrix product, arrays interprete multiplication as coefficient-wise product. For example:
+multiplication as the matrix product and arrays interpret multiplication as the coefficient-wise product. Thus, two 
+arrays can be multiplied if they have the same size.
 
-\include Tutorial_ArrayClass_mult.cpp
+<table class="tutorial_code"><tr><td>
-Output:
+Example: \include Tutorial_ArrayClass_mult.cpp
-\verbinclude Tutorial_ArrayClass_mult.out
+</td>
+<td>
+Output: \verbinclude Tutorial_ArrayClass_mult.out
+</td></tr></table>
 
 
+\section TutorialArrayClassCwiseOther Other coefficient-wise operations
+
+The Array class defined other coefficient-wise operations besides the addition, subtraction and multiplication
+operators described about. For example, the \link ArrayBase::abs() .abs() \endlink method takes the absolute
+value of each coefficient, while \link ArrayBase::sqrt() .sqrt() \endlink computes the square root of the
+coefficients. If you have two arrays of the same size, you can call \link ArrayBase::min() .min() \endlink to
+construct the array whose coefficients are the minimum of the corresponding coefficients of the two given
+arrays. These operations are illustrated in the following example.
+
+<table class="tutorial_code"><tr><td>
+Example: \include Tutorial_ArrayClass_cwise_other.cpp
+</td>
+<td>
+Output: \verbinclude Tutorial_ArrayClass_cwise_other.out
+</td></tr></table>
+
+More coefficient-wise operations can be found in the \ref QuickRefPage.
+
 
 \section TutorialArrayClassConvert Converting between array and matrix expressions
 
-It is possible to wrap a matrix expression as an array expression and conversely. This gives access to all operations
+When should you use objects of the Matrix class and when should you use objects of the Array class? You cannot
-regardless of the choice of declaring objects as arrays or as matrices.
+apply Matrix operations on arrays, or Array operations on matrices. Thus, if you need to do linear algebraic
+operations such as matrix multiplication, then you should use matrices; if you need to do coefficient-wise
+operations, then you should use arrays. However, sometimes it is not that simple, but you need to use both
+Matrix and Array operations. In that case, you need to convert a matrix to an array or reversely. This gives
+access to all operations regardless of the choice of declaring objects as arrays or as matrices.
 
-\link MatrixBase Matrix expressions \endlink have a \link MatrixBase::array() .array() \endlink method that
+\link MatrixBase Matrix expressions \endlink have an \link MatrixBase::array() .array() \endlink method that
 'converts' them into \link ArrayBase array expressions\endlink, so that coefficient-wise operations
 can be applied easily. Conversely, \link ArrayBase array expressions \endlink
 have a \link ArrayBase::matrix() .matrix() \endlink method. As with all Eigen expression abstractions,
 this doesn't have any runtime cost (provided that you let your compiler optimize).
-
 Both \link MatrixBase::array() .array() \endlink and \link ArrayBase::matrix() .matrix() \endlink 
 can be used as rvalues and as lvalues.
 
-Mixing matrices and arrays in an expression is forbidden with Eigen. However,
+Mixing matrices and arrays in an expression is forbidden with Eigen. For instance, you cannot add a amtrix and
+array directly; the operands of a \c + operator should either both be matrices or both be arrays. However,
 it is easy to convert from one to the other with \link MatrixBase::array() .array() \endlink and 
-\link ArrayBase::matrix() .matrix() \endlink.
+\link ArrayBase::matrix() .matrix()\endlink. The exception to this rule is the assignment operator: it is
+allowed to assign a matrix expression to an array variable, or to assign an array expression to a matrix
+variable.
 
-On the other hand, assigning a matrix (resp. array) expression to an array (resp. matrix) expression is allowed.
+The following example shows how to use array operations on a Matrix object by employing the 
+\link MatrixBase::array() .array() \endlink method. For example, the statement 
+<tt>result = m.array() * n.array()</tt> takes two matrices \c m and \c n, converts them both to an array, uses
+* to multiply them coefficient-wise and assigns the result to the matrix variable \c result (this is legal
+because Eigen allows assigning array expressions to matrix variables). 
 
-\subsection TutorialArrayClassInteropMatrix Matrix to array example
+As a matter of fact, this usage case is so common that Eigen provides a \link MatrixBase::cwiseProduct()
-The following example shows how to use array operations on a Matrix object by employing
+.cwiseProduct() \endlink method for matrices to compute the coefficient-wise product. This is also shown in
-the \link MatrixBase::array() .array() \endlink method:
+the example program.
 
 <table class="tutorial_code"><tr><td>
 \include Tutorial_ArrayClass_interop_matrix.cpp
@@ -143,21 +178,13 @@ Output:
 \verbinclude Tutorial_ArrayClass_interop_matrix.out
 </td></tr></table>
 
+Similarly, if \c array1 and \c array2 are arrays, then the expression <tt>array1.matrix() * array2.matrix()</tt>
+computes their matrix product.
 
-\subsection TutorialArrayClassInteropArray Array to matrix example
+Here is a more advanced example. The expression <tt>(m.array() + 4).matrix() * m</tt> adds 4 to every
-The following example shows how to use matrix operations with an Array
+coefficient in the matrix \c m and then computes the matrix product of the result with \c m. Similarly, the
-object by employing the \link ArrayBase::matrix() .matrix() \endlink method:
+expression <tt>(m.array() * n.array()).matrix() * m</tt> computes the coefficient-wise product of the matrices
-
+\c m and \c n and then the matrix product of the result with \c m.
-<table class="tutorial_code"><tr><td>
-\include Tutorial_ArrayClass_interop_array.cpp
-</td>
-<td>
-Output:
-\verbinclude Tutorial_ArrayClass_interop_array.out
-</td></tr></table>
-
-\subsection TutorialArrayClassInteropCombination Example with combinations of .array() and .matrix()
-Here is a more advanced example:
 
 <table class="tutorial_code"><tr><td>
 \include Tutorial_ArrayClass_interop.cpp

doc/examples/Tutorial_ArrayClass_accessors.cpp

@@ -10,7 +10,7 @@ int main()
   
   // assign some values coefficient by coefficient
   m(0,0) = 1.0; m(0,1) = 2.0;
-  m(1,0) = 3.0; m(1,1) = 4.0;
+  m(1,0) = 3.0; m(1,1) = m(0,1) + m(1,0);
   
   // print values to standard output
   cout << m << endl << endl;

doc/examples/Tutorial_ArrayClass_addition.cpp

@@ -8,15 +8,16 @@ int main()
 {
   ArrayXXf a(3,3);
   ArrayXXf b(3,3);
-  
   a << 1,2,3,
        4,5,6,
        7,8,9;
-
   b << 1,2,3,
        1,2,3,
        1,2,3;
        
-  cout << "a + b = " << endl
+  // Adding two arrays
-       << a + b << endl;
+  cout << "a + b = " << endl << a + b << endl << endl;
+
+  // Subtracting a scalar from an array
+  cout << "a - 2 = " << endl << a - 2 << endl;
 }

doc/examples/Tutorial_ArrayClass_addition_scalar.cpp

@@ -1,17 +0,0 @@
-#include <Eigen/Dense>
-#include <iostream>
-
-using namespace Eigen;
-using namespace std;
-
-int main()
-{
-  ArrayXXf a(3,3);
-  
-  a << 1,2,3,
-       4,5,6,
-       7,8,9;
-
-  cout << "a + 2 = " << endl
-       << a + 2 << endl;
-}

doc/examples/Tutorial_ArrayClass_cwise_other.cpp

@@ -0,0 +1,19 @@
+#include <Eigen/Dense>
+#include <iostream>
+
+using namespace Eigen;
+using namespace std;
+
+int main()
+{
+  ArrayXf a = ArrayXf::Random(5);
+  a *= 2;
+  cout << "a =" << endl 
+       << a << endl;
+  cout << "a.abs() =" << endl 
+       << a.abs() << endl;
+  cout << "a.abs().sqrt() =" << endl 
+       << a.abs().sqrt() << endl;
+  cout << "a.min(a.abs().sqrt()) =" << endl 
+       << a.min(a.abs().sqrt()) << endl;
+}

doc/examples/Tutorial_ArrayClass_interop.cpp

@@ -8,31 +8,15 @@ int main()
 {
   MatrixXf m(2,2);
   MatrixXf n(2,2);
-  
   MatrixXf result(2,2);
 
-  //initialize matrices
   m << 1,2,
        3,4;
-
   n << 5,6,
        7,8;
   
-  // mix of array and matrix operations
-  //   first coefficient-wise addition
-  //   then the result is used with matrix multiplication
   result = (m.array() + 4).matrix() * m;
-
+  cout << "-- Combination 1: --" << endl << result << endl << endl;
-  cout << "-- Combination 1: --" << endl
-    << result << endl << endl;
-
-
-  // mix of array and matrix operations
-  //   first coefficient-wise multiplication
-  //   then the result is used with matrix multiplication
   result = (m.array() * n.array()).matrix() * m;
-
+  cout << "-- Combination 2: --" << endl << result << endl << endl;
-  cout << "-- Combination 2: --" << endl
-    << result << endl << endl;
-
 }

doc/examples/Tutorial_ArrayClass_interop_array.cpp

@@ -1,34 +0,0 @@
-#include <Eigen/Dense>
-#include <iostream>
-
-using namespace Eigen;
-using namespace std;
-
-int main()
-{
-  ArrayXXf m(2,2);
-  ArrayXXf n(2,2);
-  
-  ArrayXXf result(2,2);
-
-  //initialize arrays
-  m << 1,2,
-       3,4;
-
-  n << 5,6,
-       7,8;
-
-  
-  // --> array multiplication
-  result = m * n;
-
-  cout << "-- Array m*n: --" << endl
-    << result << endl << endl;
-
-
-  // --> Matrix multiplication
-  result = m.matrix() * n.matrix();
-  
-  cout << "-- Matrix m*n: --" << endl
-    << result << endl << endl;
-}

doc/examples/Tutorial_ArrayClass_interop_matrix.cpp

@@ -8,34 +8,19 @@ int main()
 {
   MatrixXf m(2,2);
   MatrixXf n(2,2);
-  
   MatrixXf result(2,2);
 
-  //initialize matrices
   m << 1,2,
        3,4;
-
   n << 5,6,
        7,8;
 
-  
-  // --> matrix multiplication
   result = m * n;
-
+  cout << "-- Matrix m*n: --" << endl << result << endl << endl;
-  cout << "-- Matrix m*n: --" << endl
-    << result << endl << endl;
-
-
-  // --> coeff-wise multiplication
   result = m.array() * n.array();
-  
+  cout << "-- Array m*n: --" << endl << result << endl << endl;
-  cout << "-- Array m*n: --" << endl
+  result = m.cwiseProduct(n);
-    << result << endl << endl;
+  cout << "-- With cwiseProduct: --" << endl << result << endl << endl;
-  
-  
-  // ->> coeff-wise addition of a scalar
   result = m.array() + 4;
-  
+  cout << "-- Array m + 4: --" << endl << result << endl << endl;
-  cout << "-- Array m + 4: --" << endl
-    << result << endl << endl;
 }

doc/examples/Tutorial_ArrayClass_mult.cpp

@@ -8,13 +8,9 @@ int main()
 {
   ArrayXXf a(2,2);
   ArrayXXf b(2,2);
-  
   a << 1,2,
        3,4;
-
   b << 5,6,
        7,8;
-
+  cout << "a * b = " << endl << a * b << endl;
-  cout << "a * b = " << endl
-       << a * b << endl;
 }