I use words "Y" and "X" in this site. "Y" means objective variables and "X" means explanatory variables. And "Y" means result and "X" means reason. As well as I know, Quality Engineering uses these words. I use these words too because they are useful to understand more directly.
In addition, I see the formulation " Y = f(X) " in books. It means Y is the function of X. Regression Analysis uses this formulation practically. But in many books including Quality Engineering, authors use the formulation to make images of relationship between results and reasons.
Mathematics is important in engineering, In many cases, the level of mathematics in engineering is not so high. We use from elementary school level (fraction, multiplication), to first grade level of university (matrix,dirrerentiation,statistcs,probability).
But books of mathematical engineering explain state of the art mathematics. So there is a gap
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