Update README.md

README.md

@@ -43,15 +43,14 @@ The script is programmed with extended formulas for the purpose of stress-free e
  $$
 \sigma_\text{v} = \text{tr}\boldsymbol{\sigma},
  $$
-
  $$
 \sigma_\text{m} = \frac{1}{3}\sigma_\text{v}.
  $$
 
  ### Hydrostatic Stress Tensor
 
  $$
-\boldsymbol{\sigma}_\text{hyd} = \sigma_\text{m}\mathbf{I}.
+\boldsymbol{\sigma}\_\text{hyd} = \sigma\_\text{m}\mathbf{I}.
  $$
 
  ### Deviatoric Stress Tensor