There are many ways to perform linear fitting in MATLAB. This page lists some of the methods: https://www.mathworks.com/help/matlab/data_analysis/linear-regression.html.
Here are some options (out of many) from that page:
- Core MATLAB: Simple linear regression using the \ operator.
- Core MATLAB: Fit a first-order linear polynomial with polyfit. https://www.mathworks.com/help/matlab/ref/polyfit.html . Note that the "Extended Capabilities" section of the doc page mentions that polyfit supports "C/C++ Code Generation".
- With Statistics and Machine Learning Toolbox: Use fitlm. https://www.mathworks.com/help/stats/fitlm.html
You mention that you want to "perform linear fitting online". What is your deployment scenario? You can take a look at some deployment options at https://www.mathworks.com/company/newsletters/articles/selecting-a-matlab-application-deployment-strategy.html, https://www.mathworks.com/help/compiler/getting-started-with-matlab-compiler.html and https://www.mathworks.com/help/compiler/standalone-applications.html.
A more general intro to data fitting in MATLAB can be found at https://www.mathworks.com/discovery/data-fitting.html
