d W d t = p W {\displaystyle {\frac {dW}{dt}}=pW}
For Systems of ODEs
d W d t = ( p 11 + p 22 + … + p n n ) W = [ t r P ] W {\displaystyle {\frac {dW}{dt}}=(p_{11}+p_{22}+\ldots +p_{nn})W=[trP]W}