Tensor construction and initialisation

• Tensor Constructors
  • Initializer list constructors
  • Constructing Tensors from a scalar
  • Constructing Tensors from C arrays
  • Constructing from std::array/std::vector
  • Initialiser methods

Tensor Constructors

Initializer list constructors

There are many ways to construct Fastor tensors. The easiest way is using initializer lists or braces

Tensor<double,2,3> mat = {{1,2,3},
                          {4,5,6}};

You can create tensors of any order using braces for instances for a 3D tensor you do

Tensor<double,2,2,3> array_3d = {{{1,2,3},
                                  {4,5,6}},
                                  {{8,9,10},
                                  {11,12,13}}};

Note the number of opening and closing braces should match the dimension (rank) of the tensor.

Constructing Tensors from a scalar

You can initialise all values of a tensor to a given scalar if you want

Tensor<int,4,4> a(5);
Tensor<float,2,2> b(0.f);

Constructing Tensors from C arrays

If you already have data stored in a C array or a pointer you can initialise your tensor as

double c_array[4] = {1,2,3,4};
Tensor<double,4> a(c_array); // construct a vector from c_array
Tensor<double,2,2> a(c_array); // construct a matrix from c_array

Constructing from std::array/std::vector

You can also construct a tensor from a std::array or std::vector

std::array<double,4> std_array = {1,2,3,4};
Tensor<double,2,2> a(std_array); // construct a matrix from std::array

std::vector<double> std_vec = {1,2,3,4};
Tensor<double,2,2> a(std_vec); // construct a matrix from std::vector

Note that you don't have to give the size as the size and dimension of the tensor is encoded in the type of the tensor

Initialiser-methods

There are many initialiser methods provided that you can use for filling your tensors

Tensor<float,3,4,5> a;
a.zeros(); // fill all the elements with zero
a.ones(); // fill all the elements with one
a.fill(2.5); // fill all the elements with 2.5
a.random(); // fill all the elements with random numbers
a.iota(3); // fill all the elements with sequentially ascending number starting from 3
a.arange(3); // fill all the elements with sequentially ascending number starting from 3. Same as above