Sorush Khajepor - Numerical coding and app development

C++ .Net Design Algorithms Html Diverse

For scientists and numerical code developers

Develop clean, maintainable, and efficient code

Here I go beyond code syntax and equations, I explain how a language serves the project. I talk about software design, creating packages, code efficiency, conventions, and graphical user interface.

A C++ MPI code for 2D unstructured halo exchange

01 Nov 2022

I expain my code for a 2D halo exchange of unstructed mesh blocks (boxes) using message passing interface (MPI). Any thickness of halo and periodic condition are supported. The blocks can have different sizes and location in space. A CPU can run multiple blocks.

Essential bash customizations: prompt, ls, aliases, and history date

20 Aug 2022

Bash prompt is made to show more info, ls output is customized to be colorful, history date added and aliases are recommanded to enhance efficiency.

Script to copy a directory path in memory in Bash terminal

10 Aug 2022

I explain how, with a script, copy the path of current directory in memory in a Bash terminal, without a mouse, and use it for other actions.

What is the difference between .bashrc, .bash_profile, and .profile?

09 Aug 2022

The start-up Bash commands, variables, aliases and cutomizations are put in .bashrc, .bash_profile, and .profile files. So whenever you open a new terminal, one of these files is sourced first, but which one?

A C++ MPI code for 2D arbitrary-thickness halo exchange with sparse blocks

04 Jun 2022

I am writing an example of halo exchange for message passing interface (MPI). Halo exchange is usual part of high performance math and CFD solvers. The example here deals with a 2D halo of arbitrary thickness and transfers corner nodes. The blocks can be sparse in space.

Create clone of a C++ class in polymorphic way

14 May 2022

I explain how we can make a clone/copy of the object of a polymorphic pointer at runtime. A virutal clone function is created to solve this. It can return raw pionters or unique pointers. Returning raw pointers lead to covariance.

How to use type erasure pattern to decouple polymorphic classes in C++?

10 May 2022

A dependency injection explained with an example. The dynamic dispatch goes through two pointer indirection when a class and its strategies are loosely coupled. The example is recreated using template type erasure where a class and its strategies are completely decoupled.

What is tag-dispatch in C++?

01 May 2022

Tag-dispatch is a metaprogramming technique to overload a function using different tag parameters. The right overload is chosen by a compiler at compile time. It can be replaced by if-constexpr of C++17.

What is C++ metafunction and how to use it?

29 Apr 2022

In C++ metaprogramming, a metafunction receives types and/or integral values, and after performing some logics returns types and/or integral values. Metafunctions along with constexpr functions become a strong tool for metaprogramming.

What are C++ variadic templates and fold expressions?

23 Apr 2022

A variadic template is a function or class template that accepts a parameter pack. There is no explicit for-loop command to iterate the pack parameters. Since C++17, fold expressions, which are way cleaner that recursive functions, are implemented to expand parameter packs.

CMake part 3: create a config file to be found by find_package()

01 Apr 2022

In this post, I show how to create CMake config and version file for a project with an example. In this way, the user of the library can import it easily with find_package() command.

CMake part 2: Examples to build executable and library projects

30 Mar 2022

In this post, instead of throwing instructions for some random commands, I aim to explain how to employ modern CMake step by step to build executables (applications) and static/shared/header-only libraries from C++ projects.

CMake part 1: It is a programming language!

19 Mar 2022

This post aims to coherently mention important concepts, syntax, and commands of CMake as a programming language. I focus on installation, defining variables, if-conditions, loops, functions, scopes and so on.

Example for SWIG to wrap C++ library in .Net 6

12 Mar 2022

A SWIG interface is created to wrap a native C++ library and be read by .Net 6. The code is compiled using CMake. The library is used in a C# program. This setup is cross-platform and tested on Linux and Windows.

How to work with wxPython BoxSizer

11 Mar 2022

In wxPython, BoxSizer is responsible for the horizontal and vertical layout of controls such as buttons, text boxes, combo boxes, panels, and other sizers. The different layouts, alignments, and flags of BoxSizer are demonstrated with examples.

Build Clang 13 from source on Ubuntu

18 Feb 2022

I step by step show how to download clang 13 source code and install it on Ubuntu 20.04.

An MPI OpenMP example script for Slurm

15 Feb 2022

A Slurm script is created to submit a parallel code multiple times to a cluster. The commands to submit the job and check its status are shown. The program is a parallel C++ code containing MPI and OpenMP directives.

How to have detached persistent remote terminal

09 Feb 2022

With screen and tmux commands, I explain how you keep remote Linux terminals alive and running while your local machine is disconnected from the remote machine.

How to write C++ concurrent code with std::thread

21 Jan 2022

Here, I explain how To write multithread programs in C++ to run multiple tasks simultaneously. Thread objects are described with examples. Moreover, I talk about how threads are constructed, joined and detached.

What is the difference between concurrency and parallelism?

26 Dec 2021

I explain the difference between serial, concurrent, and parallel code. The processor is defined. The readers are guided on what to look for to start writing concurrent and parallel codes.

Master C++ const once and for all

11 Nov 2021

A constant object doesn’t change during program runtime. Constantness also means read-only access to an object. I expain it with examples.

Automate MPI custom type creation with C++

24 Oct 2021

Here with the aid of C++20, variadic functions, and type-traits, I created a header library to automate creation of MPI custom (derived) datatype.

C++ constexpr makes compile-time programming a breeze

23 Oct 2021

The code written with constexpr is aimed to be evaluated at compile-time.Here constexpr conditions, variables and calsses are explained.

Compile-time vs runtime programming in C++

09 Oct 2021

Here I explain the difference between compile-time and runtime in C++ with examples. being a statically typed language, C++ contains meta-programming syntax and commands that let us to program the types and constant values for just compile-time.

Use pybind11 for a detailed but simple example

30 Sep 2021

A detailed C++ project, the robot, is created. Then, its classes and their components are declared in python: constructors, methods, public data members, and setter and getter (property).

Python for file management

05 Jun 2021

I show how Python functions can be used for file management: create, delete, copy, and move files. Therefore, you can automating complex tasks with Python programming.

pybind11: call OpenMP function in Python

23 May 2021

I want to use pybind11 to compile an OpenMP parallel code. Then, I load the created module in Python and run it. The code is in C++.

Essential Linux commands to know

19 May 2021

Here, I picked essential Linux Shell commands, you need to know to use a Bash terminal: navigation, copy, delete, variables, aliases, and so on.

Journal quality x-y chart with Matplotlib

09 May 2021

I write a python script that, using Matplotlib, creates high-quality x-y charts from a CSV file. LaTeX is supported. The chart details such as font, line and marker styles and ticks are modifiable.

Build GCC 11 from source on Ubuntu

29 Apr 2021

Here I am building and installing the latest GCC, 11.1, on Ubuntu 21.04 from the source. The procedure is explained step by step.

SSH port forwarding to download files

18 Apr 2021

I want to download files from a destination computer connected to a public SSH server. The destination is accessible only via the server by SSH tunnel.

Span is a new norm in C++ codes

27 Mar 2021

Span is a new feature of C++20 for reading and writing a sequence of objects. Here, I mention how to use std::span and its functions including subspan.

Essential VS Code font and extensions for C++

14 Mar 2021

I briefly enumerate the primary font and extensions that I install on my Visual Studio (VS) Code to develop a C++ code: Fira Code font, CMake tools, bookmarks, snippets, and so on.

An overview of C++ perfect forwarding

07 Mar 2021

With a simple example, it is demonstrated that how perfect forwarding can keep rvalueness of function’s parameters. The universal reference is also discussed.

Is C++ static polymorphism useful?

28 Feb 2021

With examples, I explain static vs dynamic polymorphism. I show that static one limits the flexibility of the program at runtime. However, it can improve the performance of the code whose behaviour can be resolved at compile-time.

From lvalue, prvalue, and xvalue to move semantics in C++

21 Feb 2021

With examples, I explain the difference between lvalue, rvalue, prvalue, and xvalue. The rvalue references are defined. Consequently, I describe std::move and its application in creating move constructors and assignments.

What is a C++ weak pointer and where is it used? smart pointers part III

14 Feb 2021

Weak pointers (weak_ptr) are smart pointers that observe other objects but don’t take ownership of them. Here, I explain how they are implemented and why we need them with examples.

What is a C++ shared pointer and how is it used? smart pointers part II

07 Feb 2021

Shared pointers (shared_ptr) are smart pointers which ameliorate memory management. Here, I explain them with examples and discuss their usage and performance.

What is a C++ unique pointer and how is it used? smart pointers part I

31 Jan 2021

Unique pointers (unique_ptr) manage a pointer’s allocated memory. Here, I define them and explain the operations, passing to / returning from a function, and performance. A factory example is also demonstrated.

What are C++20 concepts and constraints? How to use them?

24 Jan 2021

With examples, C++ concepts are used to constrain template classes and functions. It is shown that concepts improve the readability of code and facilitate finding bugs.

Building a C++ project with Travis continuous integration (CI)

17 Jan 2021

I explain with an example that how a C++ project is automatically built by Travis CI with the push of a commit.

How to use C++ namespace for large projects

13 Jan 2021

I exaplain how namespaces can organize a large project and prevent name conflicts.

Create a contiguous array of a generic class in C++

10 Jan 2021

I want to create a contiguous array of a class and its derived ones. I make sure the polymorphism behavior is captured too.

A note on computer round-off error in physics

26 Dec 2020

The way floating-point numbers are stored in the memory of a computer can lead to unwanted errors. Here we have an overview of the basics of storing numbers and how they affect the outcome of physics programs.

Various ways to create arrays and vectors and their differences in C++

20 Dec 2020

Different methods to create arrays in C++ are overviewed: c-style array, pointer array, std::vector, std::array, and Boost multiarray. How the memory is managed by each style and also their practical usage is discussed.

MPI Traffic Program with C++

14 Dec 2020

I want to solve a traffic problem with MPI and C++. The road is divided into sections which send their boundaries and receive their ghost points.

Debug MPI program with Visual Studio Code

04 Dec 2020

Debugging MPI program can be a nightmare. I explain how easily you can debug a parallel MPI program with visual studio (VS) code.

C++ auto keyword makes your life easier

03 Dec 2020

In C++, auto keyword infers the type of a variable from its initializer. auto can speed up coding and improve the maintainability of code. Here, I show cases that auto can make a difference.

MPI race condition

15 Nov 2020

When a buffer, which is involved in an uncompleted non-blocking communication, is used in another communication, there will be a race to read and write the buffer.

MPI ping pong program using C++

14 Nov 2020

I want to write an MPI ping pong program where two processes send a piece of data back and forth to each other.

Handy cross-platform packages to connect to a remote Linux server

11 Nov 2020

Interaction with a remote Linux server like transferring files, editing code, or accessing the remote desktop can be much easier with these free cross-platform packages.

The difference between modes of MPI send

09 Nov 2020

There are different modes of MPI send: MPI_Send, MPI_Isend, MPI_Ssend, MPI_Bsend, and so on. They can be local or non-local, blocking or non-blocking, and synchronous or asynchronous. Their definition and differences are explained here in detail.

How and where to use C++ templates

30 Oct 2020

Using templates in C++, you can create functions or classes having similar behaviours for different types. Here, all the useful features of templates are explained with examples.

How to use Bookmark in Visual Studio

22 Oct 2020

Visual Studio bookmark speeds up code development in big projects. Here, I mention the keyboard shortcuts.

Connect to Microsoft Access database with C# .Net core

22 Oct 2020

I want to connect to an MS Access database with C# in .Net core. Therefore, I will be able to create, read, update, and delete (CRUD) records.

Lockout user after multiple failed authentication via .Net core Identity

19 Oct 2020

Goal I want to configure .Net core Identity in a way that when a user inserts wrong passwords several times the account gets locked for 5 minutes.

Add Identity pages to .Net core web app

19 Oct 2020

By default, the identity pages are pre-compiled in .Net core 3.1 and not available to be modified. I want to bring them back so they can be edited.

Create a table of content from headings of a Hugo post

17 Oct 2020

Goal I want to write code to get a table of content (ToC) for each blog post automatically. It is created and shown on the right-hand side of the content of a post.

How to add a video to a Hugo post

16 Oct 2020

I want to add a video to a Hugo blog post. The video is hosted on my website, so it is not a Youtube or Vimeo.

Tutorial: Setup of Entity Framework (EF) core for CRUD and authentication with Razor pages

10 Oct 2020

Goal In this post, step by step I create a web app using Entity Framework core and razor pages. The app is a library that admin can CRUD books info on a database and authenticated users can browse the records.

C++ inheritance crash course

03 Oct 2020

Inheritance is the mechanism that the attributes and methods of a base class are passed to a derived class. Here, all useful details of C++ inheritance are mentioned with examples.

Host a .Net core web application for less than $5 a month

02 Oct 2020

I talk about Google Cloud Platform (GCP), Microsoft Azure and Heroku. You can register with them and try their services for free or very low prices.

How to have math equations in your website

17 Jul 2020

If you want to write math equations in your website or blog, plain text becomes immediately illegible when writing something more complex than addition and subtraction.

Code LU decomposition step by step in object-oriented way in C#

28 Jun 2020

Introduction In this post I want to revisit PLU or LU decomposition or factorisation, which is used to find unknowns of a system of linear equations, for two reasons.

How Dry principle leads to clean and easy to debug code?

17 Jun 2020

Dry is short for “Don’t repeat yourself”. There are occasions that a piece of code is rewritten several times. It is better to define that as a specific method or class. I explain it with examples.

What is a recursive function?

03 Jun 2020

Definition A recursive function is a function that calls itself with different arguments. Therefore, it is applied to a problem that each step of it is similar to the previous one.

Implementing YAGNI and KISS principle to have maintainable code

03 May 2020

After reading a lot of design patterns, loose-coupling ideas, and so, you cannot wait to implement all of them in the first program you are making.

How Inversion of Control improves flexibility of numerical codes?

14 Mar 2020

Introduction When programming, it’s very convenient to create class A which has a concrete member class B. However, this creates a tightly-coupled system since any change in B should be reflected in A.

How visitor design pattern is useful for numerical programming?

09 Mar 2020

Introduction The visitor design pattern separates operations from data storage. When the efficiency and memory consumption is not of concern this design pattern is not common.

What is "object slicing" trap in C++?

26 Feb 2020

Every now and then, I switch programming language from C# to C++, I fall in the trap of object slicing. It happens when a derived object is assigned by value to a base object where the extra information in the derived object is scrapped for worst.

How to use C++ raw pointers properly?

22 Feb 2020

A pointer is an 8-byte type on a 64-bit machine that holds the memory address of a target object. Here, I mention the most useful characteristics of pointers with examples.

Create a lightweight weblog homepage with Bootstrap and Html

15 Feb 2020

I want to create a lightweight homepage of a weblog with HTML, Bootstrap and a bit of custom CSS. No javascript, no database, no WordPress is used. It should be a lightweight and fast static website.

How to create a simple component, using Blazor, HTML, and CSS: Word Block

02 Feb 2020

Using .Net Blazor, I want to create a simple word-block which is a rectangle that contains a word with an X button at its right side. Clicking on X the word-block disappears.