Rotation of Coordinates
	q Suppose the Pacific SSTs are described by values at grid points: x1, x2, x3, ...xN. We know that the xi’s are probably correlated with each other. q Now, we want to determine a new set of independent predictors zi to describe the state of Pacific SST, which are linear combinations of xi: q Mathematically, we are rotating the old set of variable (x) to a new set of variable (z) using a projection matrix (e):
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