Convergence: In numerical method, we get an approximate solution. In FEA, the error gets reduced by increasing the number of elements or the degree of polynomial. If the final solution obtained matches with the exact one expected, within permissible error we say convergence is reached.

Criteria to achieve convergence

1. The polynomial should be complete polynomial.
2. The polynomial should be continuous over the element and also differentiable upto the order of the derivate of the weak form.
3. The approximate solution should be interpolation function of primary variable at the nodes of the finite element.