👀 Views: 78 💬 Answers: 1 📅 Created: 2025-06-12

java sparse-matrix performance Java

After trying multiple solutions online, I still can't figure this out. Quick question that's been bugging me - I've looked through the documentation and I'm still confused about I'm currently implementing a sparse matrix multiplication algorithm in Java, but I'm running into performance issues when dealing with large datasets. My matrices are represented using a Map<Integer, Map<Integer, Double>> structure, where the outer map's key is the row index and the inner map's key is the column index with its corresponding value. Here's the relevant code snippet for my multiplication method: ```java public Map<Integer, Map<Integer, Double>> multiplySparseMatrices(Map<Integer, Map<Integer, Double>> matrixA, Map<Integer, Map<Integer, Double>> matrixB) { Map<Integer, Map<Integer, Double>> result = new HashMap<>(); for (Map.Entry<Integer, Map<Integer, Double>> rowA : matrixA.entrySet()) { int rowIndexA = rowA.getKey(); for (Map.Entry<Integer, Double> entryA : rowA.getValue().entrySet()) { int colIndexA = entryA.getKey(); double valueA = entryA.getValue(); if (matrixB.containsKey(colIndexA)) { for (Map.Entry<Integer, Double> entryB : matrixB.get(colIndexA).entrySet()) { int colIndexB = entryB.getKey(); double valueB = entryB.getValue(); result.putIfAbsent(rowIndexA, new HashMap<>()); result.get(rowIndexA).merge(colIndexB, valueA * valueB, Double::sum); } } } } return result; } ``` While this works correctly for smaller matrices, I face significant performance degradation when the matrices grow large (thousands of rows and columns). I suspect that the way I'm accessing the nested maps is inefficient, but I can't pinpoint which part is causing the slowdown. I've tried profiling the code using VisualVM, and it seems that a lot of time is spent in the `merge` method of the result map. Is there a more efficient way to represent and perform the multiplication on large sparse matrices in Java? Additionally, what data structures would you recommend for optimizing the access patterns and minimizing overhead? Any suggestions or best practices would be greatly appreciated! I'm working on a web app that needs to handle this. I'm on Windows 10 using the latest version of Java. Thanks for taking the time to read this!