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Where exactly does the original matrix equation XY+YX=0 enter the module verification?

The matrix equation enters at the final step of the verification computation, where the expression (XY+YX)v(XY+YX)v is evaluated. Because XX and YY are assumed to solve XY+YX=0XY+YX=0, this expression equals the zero vector, confirming that the ideal generator acts trivially.

Conditions

  • X,Y∈Mn×n(C)X,Y \in M_{n\times n}(\mathbb{C}).
  • XY+YX=0XY+YX=0.
  • The verification expands (xy+yx+I)v(xy+yx+I)v into (XY+YX)v(XY+YX)v.

Reasoning, step by step

  1. Expand the action of the ideal generator: (xy+yx+I)v=(x+I)(y+I)v+(y+I)(x+I)v(xy+yx+I)v = (x+I)(y+I)v + (y+I)(x+I)v.
  2. Apply the definition of the module action: this becomes XYv+YXvXYv + YXv.
  3. Factor out the vector: XYv+YXv=(XY+YX)vXYv + YXv = (XY+YX)v.
  4. Use the hypothesis that XX and YY solve the matrix equation: XY+YX=0XY+YX=0.
  5. Conclude that (XY+YX)v=0v=0(XY+YX)v = 0v = 0, which matches the required action of the zero element in RR.

Example

The board shows the chain of equalities ending with `= (XY+YX)v=0v = 0`, and the lecturer notes that this is zero 'since it's a solution to this equation star'.

Common misconceptions

  • Thinking the matrix equation is used to define the ring RR.
  • Assuming the verification fails if XX and YY do not commute.

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