I will present a numerical and observational approach to studying the structure and internal physics of quasar accretion disks (AD) using two types of disk reverberation mapping (RM). The first is the traditional continuum RM, which measures lags in the variability of quasar light curves from high to low frequency wave bands on the light-crossing time scale due to the reprocessing of light in different temperature regions of the disk. This method has been used for decades, however, the transfer function of this reprocessing and how it can be affected by local variability in the disk are not well understood. Multi-frequency radiation magnetohydrodynamic codes make it possible to directly simulate the reprocessing of light by a quasar disk. I will present results from new radiation Athena++ simulations and discuss how they can be directly compared to observations to better understand reprocessing. I will also discuss a second type of lag, the “long negative lag.” The long negative lag occurs when fluctuations in the outer UV/optical region of the disk are accreted inward on the longer inflow timescale leading variability from these fluctuations in high frequency bands to lag the corresponding variability at low frequency. Because the inflow rate, unlike the speed of light, also depends on disk properties, long lags can provide additional information about disk structure. I will outline the underlying theory of these long lags, present several possible detections, and discuss the prospect of detecting more in the near future with the Vera C. Rubin Observatory.