Prim Algorithm Calculator

Build the lightest network across all vertices. Review chosen edges, running cost, and spanning structure. Plot weights, export reports, and inspect each selection clearly.

Enter graph details

Use a stacked page layout, while the calculator fields flow in 3 columns on large screens, 2 on medium screens, and 1 on small screens.

Separate names with commas or new lines. You may leave this list as-is and focus on the edges.
Use one undirected edge per line in the format Vertex1,Vertex2,Weight.
Prim's method can start anywhere on a connected graph.
Choose how many decimal places appear in tables and exports.
Accepted format example
A,B,4
B,C,1
C,D,5

Formula used

Prim's algorithm expands a tree by repeatedly selecting the lightest edge that connects one included vertex to one excluded vertex.

Selection rule

Choose e = (u, v) with minimum w(e), where u is already in the tree and v is outside it.

Total tree weight

W(T) = Σ w(e) for every edge selected into the spanning tree.

For a connected graph with V vertices, the final tree contains exactly V - 1 edges and no cycles. The code uses an adjacency matrix approach, which is practical for small and medium graphs and follows a time complexity near O(V²).

How to use this calculator

  1. Enter the vertex names, or let the edge list define them automatically.
  2. Type one weighted edge per line using the pattern Vertex1,Vertex2,Weight.
  3. Choose a start vertex and optional decimal precision.
  4. Press Calculate Prim Tree to place the result below the header and above the form.
  5. Review the MST edges, cumulative totals, adjacency matrix, and graph density.
  6. Download the CSV or PDF file when you need a report.

Example data table

Edge Weight Comment
A - B 4 Connects the first pair of vertices.
B - C 1 Very light edge, often chosen early.
B - D 2 Links a new branch with low cost.
D - E 5 Adds another vertex to the tree.
E - F 2 Finishes the connection with low weight.

Frequently asked questions

1) What does this calculator return?

It returns the minimum spanning tree, total tree weight, ordered edge selections, cumulative cost, adjacency matrix, graph density, and exportable summary tables.

2) Does the start vertex change the final weight?

For a connected graph with unique edge decisions, the total minimum weight remains the same. Different equal-weight ties can change edge order or structure, but still produce a valid minimum spanning tree.

3) Can I enter decimal edge weights?

Yes. The parser accepts integers and decimals. Use the precision field to control how many decimal places appear in the displayed tables and download files.

4) What happens when the graph is disconnected?

A single spanning tree cannot cover every vertex. The calculator highlights that condition and shows which vertices were left outside the tree so you can add missing connecting edges.

5) Why are duplicate edges reduced?

If the same undirected pair appears more than once, the calculator keeps the smallest weight. That reflects the cheapest available direct connection between those two vertices.

6) Is Prim's algorithm the same as Dijkstra's method?

No. Prim's algorithm minimizes the total weight of a spanning tree. Dijkstra's method minimizes shortest-path distance from one source vertex to every reachable vertex.

7) How many edges should a valid tree contain?

For a connected graph with V vertices, any spanning tree must contain exactly V minus 1 edges. More edges create cycles, and fewer edges leave the graph disconnected.

8) When should I use Prim's algorithm?

Use it when you need the cheapest network without cycles, such as cable routing, road design, pipe layouts, cluster linking, or other weighted graph problems.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.