数值分析中，一个问题的条件数是该数量在数值计算中的容易程度的衡量，也就是该问题的适定性。一个低条件数的问题称为良置的，而高条件数的问题称为病态（或者说非良置）的。

In the field of numerical analysis, the condition number of a function with respect to an argument measures how much the output value of the function can change for a small change in the input argument. This is used to measure how sensitive a function is to changes or errors in the input, and how much error in the output results from an error in the input. Very frequently, one is solving the inverse problem – given one is solving for x, and thus the condition number of the (local) inverse must be used. In linear regression the condition number can be used as a diagnostic for multicollinearity.