Ansatz

Ansatz (Ger., "anset, onset, or outset"; plural: Ansätze) is a term often used by physicists and mathematicians. An ansatz is the establishment of the starting equation(s) describing a mathematical or physical problem. It can take into consideration boundary conditions. After an ansatz has been established, the equations are solved for the general function of interest. Typically, a word problem starts by writing down the ansatz with subsequent refinement leading to the solution of the problem. An ansatz is a wise guess that is legitimated later by its results.
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n. beginning, start, commencement