The cumulative distribution function (CDF) of the doubly non-central beta distribution can be expressed as an infinite double series. By truncating the sum of this series, one can obtain an approximate value of the CDF. Although numerous methods exist for calculating the non-central beta distribution, which allow for the control of the truncation range and estimation of the computational error, no such methods have been developed for the doubly non-central beta distribution. In this paper, we propose two new numerical computation methods based on the segmentation of the infinite double series, termed DIV1 and DIV2. Both methods enable automated calculations once the error control parameters are set; there is no need to predetermine the truncation range, and their computational times are comparable. Following detailed derivations, we have established the upper bounds of the errors for both methods, thus ensuring the determinability of the precision.

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