R包中可以看到IRT的代码
https://cran.r-project.org/web/packages/ltm/index.html
Analysis of multivariate dichotomous and polytomous data using latent trait models under the Item Response Theory approach. It includes the Rasch, the Two-Parameter Logistic, the Birnbaum's Three-Parameter, the Graded Response, and the Generalized Partial Credit Models.

https://cran.r-project.org/web/packages/TAM/index.html

Includes marginal and joint maximum likelihood estimation of uni- and multidimensional item response models (Rasch, 2PL, 3PL, Generalized Partial Credit, Multi Facets, Nominal Item Response, Structured Latent Class Analysis, Mixture Distribution IRT Models, Located Latent Class Models). Latent regression models and plausible value imputation are also supported.

https://cran.r-project.org/web/packages/eRm/index.html

The eRm package fits Rasch models (RM), linear logistic test models (LLTM), rating scale model (RSM), linear rating scale models (LRSM), partial credit models (PCM), and linear partial credit models (LPCM). Missing values are allowed in the data matrix. Additional features are the ML estimation of the person parameters, Andersen's LR-test, item-specific Wald test, Martin-Löf-Test, nonparametric Monte-Carlo Tests, itemfit and personfit statistics including infit and outfit measures, various ICC and related plots, automated stepwise item elimination, simulation module for various binary data matrices. An eRm platform is provided at R-forge (see URL).

有源码好啊，希望有源码的多奉献啊

一般研究者是不太会将自己的原始代码放出来的，如果需要看代码，可将R语言中irt包打开看