Here is the code that does what I explained. I just switched up step 5 with
a much simpler approach. Note that you can simply make this into a
function/class template so that you could read general tensors, not just
3x3 tensors. I leave that to you :-)
#include <deal.II/base/tensor.h>
#include <deal.II/base/parameter_handler.h>
#include <deal.II/base/utilities.h>
#include <string>
#include <iostream>
#include <sstream>
using namespace dealii;
int main() {
// Let's read this tensor from an istringstream. You may read it from
istream in your
// application
std::istringstream is("set Tensor3x3 = 11, 12, 13, 21, 22, 23, 31, 32, 33");
// Now let's set up the ParameterHandler object. Since you are reading 3x3
tensor, you are
// dealing with 9 components and the default value should also have 9
components (here 9
// zeros) in it
ParameterHandler prm;
using Patterns::List;
using Patterns::Double;
prm.declare_entry("Tensor3x3",
"0,0,0,0,0,0,0,0,0",
List(Double(), 9, 9),
"Tensor components");
// Let's read it in now
prm.parse_input(is);
const std::string tensorString = prm.get("Tensor3x3");
// Now let's split the string into individual components
const std::vector<std::string> tensorComponentsString =
Utilities::split_string_list(tensorString);
// Now go over each component, convert it into double and put it in the
tensor
Tensor<2, 3> tensor;
unsigned int counter = 0;
for (unsigned ii = 0; ii < tensor.dimension; ++ii) {
for (unsigned jj = 0; jj < tensor.dimension; ++jj) {
tensor[ii][jj] =
Utilities::string_to_double(tensorComponentsString[counter++]);
}
}
// Let's check if we read the tensor correctly
for (unsigned ii = 0; ii < tensor.dimension; ++ii) {
for (unsigned jj = 0; jj < tensor.dimension; ++jj) {
std::cout << "component [" << ii << ", " << jj << " ] = "
<< tensor[ii][jj] << std::endl;
}
}
}
On Wednesday, April 15, 2020 at 3:54:57 AM UTC-4, Paras Kumar wrote:
>
> Ahmad,
>
> On Tuesday, April 14, 2020 at 5:39:06 PM UTC+2, Ahmad Shahba wrote:
>>
>> I don't know if it is the optimal way but I would use the following
>> approach
>>
>> 1. Read tensor components as Patterns::List
>> 2. Use get
>>
>> <https://www.dealii.org/current/doxygen/deal.II/classParameterHandler.html#a91cfbaca954f444047302446a4e87125>
>>
>> method of ParameterHandler to read all tensor components as one string
>> into a string variable
>> 3. Use split_string_list
>>
>> <https://www.dealii.org/current/doxygen/deal.II/namespaceUtilities.html#a0a2b9ceded96f25b47eccd7c177dc67e>
>> in the Utilities namespace to split the string into individual
>> components (still all components are strings)
>> 4. Convert string-type components into doubles using
>> string_to_double
>>
>> <https://www.dealii.org/current/doxygen/deal.II/namespaceUtilities.html#ab3177021843ad87857e6f8c5d98d29a5>
>> in
>> the Utilities namespace
>> 5. Use Tensor
>>
>> <https://www.dealii.org/current/doxygen/deal.II/classTensor.html#a6118e90e58ca4041ba452ab647db0b29>
>> (const Tensor
>> <https://www.dealii.org/current/doxygen/deal.II/classTensor.html><
>> rank_, dim, OtherNumber > &initializer) to construct the tensor
>>
>> Could you please elaborate on pointa 1 and 5, or share a code snippet
> which explains the process.
>
> Best,
> Paras
>
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