**Bilinear interpolation** (or **double interpolation**) - it is all too most as linear interpolation, only interpolation occurs simultaneously for two heteronymic functions of two variables. Ie first calculates one side of a single variable and based on the result and the value of the other unknown side to be (interpoliruetsya) the overall result.

## Short bilinear interpolation algorithm:

To interpolate value of the function at the point P, it is necessary to know values of surrounding points: Q

_{11}, Q_{12}, Q_{21}, Q_{11}

First step is to find a ancillary point R

_{1}и R_{2}by means of linear interpolation. (In truth, you can start from any side. Suppose a point R_{3}, R_{4})Through linear interpolation between the auxiliary points R

_{1}и R_{2}find value of the function at point P: