06_tensor

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0. Preface

The previous section discussed some code details based on the Vector class. This section discusses the Tensor class.

This section primarily discusses:

Discussing parts of the implementation of the Tensor class
Understanding the compilation and linking of multi-class complex libraries
Compiling and running a tensor project

1. Tensor Class

API page: https://api.openfoam.com/2506/classFoam_1_1Tensor.html

Run the following command in the terminal to search locally:

terminal

find $FOAM_SRC -iname tensor

Run the following command to open the class folder:

terminal

code $FOAM_SRC/OpenFOAM/primitives/Tensor

The file structure of this class is as follows:

terminal

tree -L 1
.
├── floats
├── ints
├── lists
├── Tensor.H
└── TensorI.H

Examine Tensor/Tensor.H to see the implementation details of this class. We will not go through it line by line here.

We can also use the API or the terminal to find and read related classes:

dimensionedTensor
tensorField

Warning

Do not delve into code details at this stage; a general understanding of the usage of member functions is sufficient.

2. OFextension Plugin

It is highly recommended to install the community plugin OFextension in VS Code.

2.1. Configuring the Plugin

Click the gear icon in the lower-left corner of VS Code to open Settings.
Search for ofextension in the search bar.
Set the correct OpenFOAM path in Ofextension: OFpath.
Open the user’s development application with VS Code, press F1, enter ofInit to initialize the configuration.

2.2. Using the Plugin

During project development, for example, in the main source code of this section, when entering relevant objects, VS Code will automatically pop up available methods (member functions).

Moreover, in the main source code, you can select header files, classes, etc., right-click, and use Go to Definition or Go to Declaration to directly jump to the source code.

This plugin is highly recommended for its convenience. Be careful not to initialize it in the OpenFOAM source folder.

Warning

Sometimes the jumped source code may not point to the correct location; pay attention to distinguish.

3. Project Setup

Run the following commands in the terminal to create the project for this section:

terminal

ofsp
mkdir ofsp_06_tensor
code ofsp_06_tensor

Continue using terminal commands or the VS Code interface to create additional files. The final file structure is as follows:

terminal

tree
.
├── Aerosand
│   ├── class1
│   │   ├── class1.C
│   │   └── class1.H
│   ├── class2
│   │   ├── class2.C
│   │   └── class2.H
│   └── Make
│       ├── files
│       └── options
├── Make
│   ├── files
│   └── options
└── ofsp_06_tensor.C

Note that the file structure of the development library is slightly different from the previous section. We have already observed that under an OpenFOAM library, there are generally multiple sub-libraries/classes. A user’s development library may also consist of several classes, and the development library has its own Make file to manage multiple classes. For example, here the Aerosand library has three classes: class1, class2, and class3.

4. Development Library

4.1. class1

For the first class, we still use the previous code.

The code in class1.H is:

/Aerosand/class1/class1.H

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#pragma once

class class1
{
private:
    double localTime_;

public:
    void SetLocalTime(double t);
    double GetLocalTime() const;
};

The code in class1.C is:

/Aerosand/class1/class1.C

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#include "class1.H"

void class1::SetLocalTime(double t) {
    localTime_ = t;
}

double class1::GetLocalTime() const {
    return localTime_;
}

4.2. class2

For the second class, we attempt to create a new class through inheritance.

The code in class2.H is:

/Aerosand/class2/class2.H

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#pragma once

#include "vector.H"

namespace Foam
{

class class2 : public vector
{
public:
    // Inherit constructors
    using Foam::vector::vector;

    // Compute the sum of components
    Foam::scalar sum() const;
};

} // namespace Foam

The code in class2.C is:

/Aerosand/class2/class2.C

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#include "class2.H"

namespace Foam
{

Foam::scalar class2::sum() const
{
    return this->x() + this->y() + this->z();
}

} // namespace Foam

Tip

Note that scalar and vector used in the declaration and definition belong to the Foam namespace, so the namespace must be used.

4.3. class3

For the third class, we write some simple content.

The code in class3.H is:

/Aerosand/class3/class3.H

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#pragma once

class class3
{
public:
    void class3Info() const;
};

The code in class3.C is:

/Aerosand/class3/class3.C

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#include "class3.H"

#include <iostream>

void class3::class3Info() const 
{
    std::cout << "This is class3\n" << std::endl;
}

4.4. Library Make

The library Make/files is:

/Aerosand/Make/files

class1/class1.C
class2/class2.C
class3/class3.C

LIB = $(FOAM_USER_LIBBIN)/libAerosand

This development library has no other dependencies; the library Make/options can be left empty.

4.5. Library Compilation

Run the following commands in the terminal to compile the library:

terminal

wclean Aerosand
wmake Aerosand

5. Main Project

5.1. Main Source Code

The code in ofsp_06_tensor.C is:

/ofsp_06_tesnsor.C

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#include "tensor.H"
#include "dimensionedTensor.H"
#include "tensorField.H"
// Including OpenFOAM classes

#include "class1.H"
#include "class2.H"
#include "class3.H"
// Including classes from the development library

using namespace Foam;

int main()
{
    scalar s(3.14); // scalar class is indirectly included via tensor.H
    vector v1(1, 2, 3); // vector class is indirectly included via tensor.H
    vector v2(0.5, 1, 1.5);
    
    // Using member functions of the tensor class below
    
    Info<< s << " * " << v1 << " = "  << s * v1 << nl 
        << "pos(s): " << pos(s) << nl
        << "asinh(s): " << Foam::asinh(s) << nl
        << endl;

    tensor T(11, 12, 13, 21, 22, 23, 31, 32, 33);
    Info<< "T: " << T << nl 
        << "Txy: " << T.xy() << nl
        << endl;

    tensor T1(1, 2, 3, 4, 5, 6, 7, 8, 9);
    tensor T2(1, 2, 3, 1, 2, 3, 1, 2, 3);
    tensor T3 = T1 + T2;
    Info<< "T3: " << T3 << nl << endl;

    tensor T4(3, -2, 1, -2, 2, 0, 1, 0, 4);
    Info<< "T4': " << inv(T4) << nl
        << "T4' * T4: " << (inv(T4) & T4) << nl
        << "T4.x(): " << T4.x() << nl
        << "T4.y(): " << T4.y() << nl
        << "T4.z(): " << T4.z() << nl
        << "T4^T: " << T4.T() << nl
        << "det(T4): " << det(T4) << nl
        << endl;

	// Using member functions of the dimensionedTensor class below
	
    dimensionedTensor sigma
    (
        "sigma",
        dimensionSet(1, -2, -2, 0, 0, 0, 0),
        tensor(1e6, 0, 0, 0, 1e6, 0, 0, 0, 1e6)
    );
    Info<< "sigma: " << sigma << nl 
        << "sigma name: " << sigma.name() << nl
        << "sigma dimension: " << sigma.dimensions() << nl
        << "sigma value: " << sigma.value() << nl
        << "sigma yy value: " << sigma.value().yy() << nl
        << endl;

	// Using member functions of the tensorField class below
	
    tensorField tf(2, tensor::one);
    Info<< "tf: " << tf << endl;
    tf[0] = tensor(1, 2, 3, 4, 5, 6, 7, 8, 9);
    tf[1] = T2;
    Info << "tf: " << tf << nl
        << "2.0 * tf" << 2.0 * tf << nl
        << endl;

	label a = 1;
    scalar pi = 3.1415926;
    Info<< "Hi, OpenFOAM!" << " Here we are." << nl
	    << a << " + " << pi << " = " << a + pi << nl
	    << a << " * " << pi << " = " << a * pi << nl
	    << endl;

	// class1 construction and output
    class1 mySolver;
    mySolver.SetLocalTime(0.2);
    Info<< "\nCurrent time step is : " << mySolver.GetLocalTime() << endl;
	
	// class2 construction and output
	class2 v3(2,4,6); // class2 inherits the constructor from vector
    Info<< "Sum of vector components: " << v3.sum() << endl;

	// class3 construction and output
    class3 myMessage;
    myMessage.class3Info();

    return 0;
}

5.2. Project Make

The project Make/files is:

/Make/files

ofsp_06_tensor.C

EXE = $(FOAM_USER_APPBIN)/ofsp_06_tensor

The project Make/options is:

/Make/options

EXE_INC = \
    -IAerosand/lnInclude

EXE_LIBS = \
    -L$(FOAM_USER_LIBBIN) \
    -lAerosand

Similarly, the $FOAM_SRC/OpenFOAM library is automatically included as a dependency; any classes used from it do not require the user to link again.

6. Compilation and Execution

Run the following commands in the terminal to compile and run the project:

terminal

wclean
wmake
ofsp_06_tensor

The output is as follows:

terminal

3.14 * (1 2 3) = (3.14 6.28 9.42)
pos(s): 1
asinh(s): 1.86181

T: (11 12 13 21 22 23 31 32 33)
Txy: 12

T3: (2 4 6 5 7 9 8 10 12)

T4': (1.33333 1.33333 -0.333333 1.33333 1.83333 -0.333333 -0.333333 -0.333333 0.333333)
T4' * T4: (1 0 0 1.66533e-16 1 0 -5.55112e-17 0 1)
T4.x(): (3 -2 1)
T4.y(): (-2 2 0)
T4.z(): (1 0 4)
T4^T: (3 -2 1 -2 2 0 1 0 4)
det(T4): 6

sigma: sigma [1 -2 -2 0 0 0 0] (1e+06 0 0 0 1e+06 0 0 0 1e+06)
sigma name: sigma
sigma dimension: [1 -2 -2 0 0 0 0]
sigma value: (1e+06 0 0 0 1e+06 0 0 0 1e+06)
sigma yy value: 1e+06

tf: 2{(1 1 1 1 1 1 1 1 1)}
tf: 2((1 2 3 4 5 6 7 8 9) (1 2 3 1 2 3 1 2 3))
2.0 * tf2((2 4 6 8 10 12 14 16 18) (2 4 6 2 4 6 2 4 6))

Hi, OpenFOAM! Here we are.
1 + 3.14159 = 4.14159
1 * 3.14159 = 3.14159


Current time step is : 0.2
Sum of vector components: 12
This is class3

7. Summary

This section has completed the following discussions:

Discussing parts of the implementation of the Tensor class
Understanding the compilation and linking of multi-class complex libraries
Compiling and running a tensor project

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Course (text, images, etc.)：CC BY-NC-SA 4.0
Code derived from OpenFOAM：GPL v3
Other code：MIT License

Last updated on March 27, 2026 • Aerosand

05_vector 07_firstApp