# RF-CONCRETE Surfaces Version 5

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# 2.7.9 Positive Definite Test

### Positive Definite Test

The positive definite of the material stiffness matrix D is tested by a modified Sylvester's criterion (with respect to the blocks of zeros). If the stiffness matrix D is not positive definite, the non-diagonal components of the material stiffness matrix are consecutively set to zero. In extreme cases, only the positive components from the diagonal remain.