If potential-equation right side equals -4 * pi * (energy density), rather than zero, equation describes gravitation and electrostatics {Poisson's equation} {Poisson equation}. Energy density is pressure.
Mathematical Sciences>Calculus>Differential Equation>Kinds>Partial>Potential
3-Calculus-Differential Equation-Kinds-Partial-Potential
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Date Modified: 2022.0224