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Learn how to effectively index a matrix in MATLAB using logical conditions from two separate matrices. This guide will walk you through the process step by step!
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This video is based on the question https://stackoverflow.com/q/62501672/ asked by the user 'Nikit Parakh' ( https://stackoverflow.com/u/13354191/ ) and on the answer https://stackoverflow.com/a/62501957/ provided by the user 'beaker' ( https://stackoverflow.com/u/1377097/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Index a Matrix in MATLAB Based on Conditions from Two Other Matrices

Are you working with matrices in MATLAB and need to extract specific values based on conditions? If so, you've come to the right place! In this article, we'll look at a practical example of how to index a matrix using conditions derived from two other matrices.

The Problem at Hand

Suppose you have the following three matrices:

[[See Video to Reveal this Text or Code Snippet]]

Your goal is to create a new matrix by indexing matrix c under specific conditions that refer back to matrices a and b. In this case, the conditions are:

Elements of a should be less than or equal to 5

Elements of b should be greater than or equal to 6

If both conditions hold for any index, you will copy the corresponding value from matrix c. If not, that position in the resulting matrix should default to zero. The expected resulting matrix after applying these conditions would look like this:

[[See Video to Reveal this Text or Code Snippet]]

A Step-By-Step Solution

Let's dive into how we can achieve this using logical indexing in MATLAB.

Step 1: Initialize Your Matrices

Start by defining your matrices a, b, and c as follows:

[[See Video to Reveal this Text or Code Snippet]]

Next, create a placeholder for your result matrix filled with zeros. This can be done easily by using the zeros function:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Create Logical Conditions

Now let's establish the logical conditions based on your original matrices a and b. You can achieve this by using logical operators like this:

[[See Video to Reveal this Text or Code Snippet]]

This statement creates a logical matrix d, where each position will evaluate to true (or 1) only if both conditions are satisfied. The resulting logical matrix d would be:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Index the Result Matrix

The final step is to copy values from matrix c to result using logical indexing. You can accomplish this with the following code:

[[See Video to Reveal this Text or Code Snippet]]

This line effectively says: "For all positions where d is true, the corresponding values from c should fill in result." Finally, your resulting matrix result will be:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

That's it! By following these steps, you can efficiently index a matrix in MATLAB based on conditions set from two other matrices. This technique is particularly useful when dealing with large datasets where you want to filter values based on specific criteria.

Feel free to experiment with different matrices and conditions to gain a deeper understanding of this concept. Happy coding!