Last updated: 2025-04-08

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Introduction

In this example, we test out symEBcovMF on tree-structured data.

Example

library(ebnm)
library(pheatmap)
library(ggplot2)

source('code/symebcovmf_functions.R')
source('code/visualization_functions.R')

Data Generation

sim_4pops <- function(args) {
  set.seed(args$seed)
  
  n <- sum(args$pop_sizes)
  p <- args$n_genes
  
  FF <- matrix(rnorm(7 * p, sd = rep(args$branch_sds, each = p)), ncol = 7)
  # if (args$constrain_F) {
  #   FF_svd <- svd(FF)
  #   FF <- FF_svd$u
  #   FF <- t(t(FF) * branch_sds * sqrt(p))
  # }
  
  LL <- matrix(0, nrow = n, ncol = 7)
  LL[, 1] <- 1
  LL[, 2] <- rep(c(1, 1, 0, 0), times = args$pop_sizes)
  LL[, 3] <- rep(c(0, 0, 1, 1), times = args$pop_sizes)
  LL[, 4] <- rep(c(1, 0, 0, 0), times = args$pop_sizes)
  LL[, 5] <- rep(c(0, 1, 0, 0), times = args$pop_sizes)
  LL[, 6] <- rep(c(0, 0, 1, 0), times = args$pop_sizes)
  LL[, 7] <- rep(c(0, 0, 0, 1), times = args$pop_sizes)
  
  E <- matrix(rnorm(n * p, sd = args$indiv_sd), nrow = n)
  Y <- LL %*% t(FF) + E
  YYt <- (1/p)*tcrossprod(Y)
  return(list(Y = Y, YYt = YYt, LL = LL, FF = FF, K = ncol(LL)))
}

sim_args = list(pop_sizes = rep(40, 4), n_genes = 1000, branch_sds = rep(2,7), indiv_sd = 1, seed = 1)
sim_data <- sim_4pops(sim_args)

This is a heatmap of the scaled Gram matrix:

plot_heatmap(sim_data$YYt, colors_range = c('blue','gray96','red'), brks = seq(-max(abs(sim_data$YYt)), max(abs(sim_data$YYt)), length.out = 50))

This is a scatter plot of the true loadings matrix:

pop_vec <- c(rep('A', 40), rep('B', 40), rep('C', 40), rep('D', 40))
plot_loadings(sim_data$LL, pop_vec)

symEBcovMF

symebcovmf_tree_fit <- sym_ebcovmf_fit(S = sim_data$YYt, ebnm_fn = ebnm_point_exponential, K = 7, maxiter = 100, rank_one_tol = 10^(-8), tol = 10^(-8))

[1] "Warning: scaling factor is zero"
[1] "Adding factor 4 does not improve the objective function"

Progression of ELBO

symebcovmf_tree_full_elbo_vec <- symebcovmf_tree_fit$vec_elbo_full[!(symebcovmf_tree_fit$vec_elbo_full %in% c(1:length(symebcovmf_tree_fit$vec_elbo_K)))]
ggplot() + geom_line(data = NULL, aes(x = 1:length(symebcovmf_tree_full_elbo_vec), y = symebcovmf_tree_full_elbo_vec)) + xlab('Iter') + ylab('ELBO')

Visualization of Estimate

This is a scatter plot of \(\hat{L}\), the estimate from symEBcovMF:

bal_pops <- c(rep('A', 40), rep('B', 40), rep('C', 40), rep('D', 40))
plot_loadings(symebcovmf_tree_fit$L_pm %*% diag(sqrt(symebcovmf_tree_fit$lambda)), bal_pops)

This is the objective function value attained:

symebcovmf_tree_fit$elbo

[1] -32163.04

Visualization of Fit

This is a heatmap of \(\hat{L}\hat{\Lambda}\hat{L}'\):

symebcovmf_tree_fitted_vals <- tcrossprod(symebcovmf_tree_fit$L_pm %*% diag(sqrt(symebcovmf_tree_fit$lambda)))
plot_heatmap(symebcovmf_tree_fitted_vals, brks = seq(0, max(symebcovmf_tree_fitted_vals), length.out = 50))

This is a scatter plot of fitted values vs. observed values for the off-diagonal entries:

diag_idx <- seq(1, prod(dim(sim_data$YYt)), length.out = ncol(sim_data$YYt))
off_diag_idx <- setdiff(c(1:prod(dim(sim_data$YYt))), diag_idx) 

ggplot(data = NULL, aes(x = c(sim_data$YYt)[off_diag_idx], y = c(symebcovmf_tree_fitted_vals)[off_diag_idx])) + geom_point() + ylim(-1, 15) + xlim(-1,15) + xlab('Observed Values') + ylab('Fitted Values') + geom_abline(slope = 1, intercept = 0, color = 'red')

Visualization of Residual Matrix

symebcovmf_tree_resid <- sim_data$YYt - symebcovmf_tree_fitted_vals
plot_heatmap(symebcovmf_tree_resid, colors_range = c('blue','gray96','red'), brks = seq(-max(abs(symebcovmf_tree_resid)), max(abs(symebcovmf_tree_resid)), length.out = 50))

Observations

symEBcovMF struggles in the tree setting. Similar to EBMFcov, symEBcovMF only recovers three factors, one intercept factor and two subtype specific factors. I suspect symEBcovMF has similar issues to EBMFcov where the residual matrix has large chunks of negative entries that cause it to not add anymore factors.

symEBcovMF with refit step

symebcovmf_tree_refit_fit <- sym_ebcovmf_fit(S = sim_data$YYt, ebnm_fn = ebnm_point_exponential, K = 7, maxiter = 100, rank_one_tol = 10^(-8), tol = 10^(-8), refit_lam = TRUE)

Progression of ELBO

symebcovmf_tree_refit_full_elbo_vec <- symebcovmf_tree_refit_fit$vec_elbo_full[!(symebcovmf_tree_refit_fit$vec_elbo_full %in% c(1:length(symebcovmf_tree_refit_fit$vec_elbo_K)))]
ggplot() + geom_line(data = NULL, aes(x = 1:length(symebcovmf_tree_refit_full_elbo_vec), y = symebcovmf_tree_refit_full_elbo_vec)) + xlab('Iter') + ylab('ELBO')

A note: I don’t think I save the ELBO value after the refitting step in vec_elbo_full. But the refitting does change this vector since it changes the residual matrix that is used when you add a new vector.

Visualization of Estimate

This is a scatter plot of \(\hat{L}_{refit}\), the estimate from symEBcovMF:

bal_pops <- c(rep('A', 40), rep('B', 40), rep('C', 40), rep('D', 40))
plot_loadings(symebcovmf_tree_refit_fit$L_pm %*% diag(sqrt(symebcovmf_tree_refit_fit$lambda)), bal_pops)

This is the objective function value attained:

symebcovmf_tree_refit_fit$elbo

[1] -11576.24

Visualization of Fit

This is a heatmap of \(\hat{L}_{refit}\hat{\Lambda}_{refit}\hat{L}_{refit}'\):

symebcovmf_tree_refit_fitted_vals <- tcrossprod(symebcovmf_tree_refit_fit$L_pm %*% diag(sqrt(symebcovmf_tree_refit_fit$lambda)))
plot_heatmap(symebcovmf_tree_refit_fitted_vals, brks = seq(0, max(symebcovmf_tree_refit_fitted_vals), length.out = 50))

This is a scatter plot of fitted values vs. observed values for the off-diagonal entries:

diag_idx <- seq(1, prod(dim(sim_data$YYt)), length.out = ncol(sim_data$YYt))
off_diag_idx <- setdiff(c(1:prod(dim(sim_data$YYt))), diag_idx) 

ggplot(data = NULL, aes(x = c(sim_data$YYt)[off_diag_idx], y = c(symebcovmf_tree_refit_fitted_vals)[off_diag_idx])) + geom_point() + ylim(-1, 15) + xlim(-1,15) + xlab('Observed Values') + ylab('Fitted Values') + geom_abline(slope = 1, intercept = 0, color = 'red')

Visualization of Residual Matrix

For comparison, I also plot a heatmap of \(S - \sum_{k=1}^{3} \hat{\lambda}_k \hat{\ell}_k \hat{\ell}_k\) where \(\hat{\lambda}_k\) and \(\hat{\ell}_k\) are estimates from symEBcovMF with the refitting step:

symebcovmf_tree_refit_resid <- sim_data$YYt - tcrossprod(symebcovmf_tree_refit_fit$L_pm[,c(1:3)] %*% diag(sqrt(symebcovmf_tree_refit_fit$lambda[1:3])))
plot_heatmap(symebcovmf_tree_refit_resid, colors_range = c('blue','gray96','red'), brks = seq(-max(abs(symebcovmf_tree_refit_resid)), max(abs(symebcovmf_tree_resid)), length.out = 50))

Observations

We see that symEBcovMF with the refitting step does a better job at recovering the hierarchical structure of the data. The loadings estimate does not look entirely binary, but this is to be expected since we used the point-exponential prior. One could imagine a procedure where you start with a fit using point-exponential prior, and then refine the estimates using the generalized binary prior.

I did try symEBcovMF with refitting with the generalized binary factor, and it yields a different representation. The first factor is an intercept like factor and the next two factors are subtype-effect factors. Factor 5 is a population effect factor. However, factors 4, 6, and 7 are not population effects. I think the method found a different representation for the four population effects (which is something I’ve seen in other examples). I’m not sure why the point-exponential prior and the generalized binary prior led to different representations. Perhaps the point-exponential prior is better at yielding sparser solutions? This would also motivate a procedure that uses point-exponential as an initialization and then uses generalized binary to make the loadings more binary.

sessionInfo()

R version 4.3.2 (2023-10-31)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Sonoma 14.4.1

Matrix products: default
BLAS:   /Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/lib/libRblas.0.dylib 
LAPACK: /Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.11.0

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

time zone: America/Chicago
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] ggplot2_3.5.1   pheatmap_1.0.12 ebnm_1.1-34     workflowr_1.7.1

loaded via a namespace (and not attached):
 [1] gtable_0.3.5       xfun_0.48          bslib_0.8.0        processx_3.8.4    
 [5] lattice_0.22-6     callr_3.7.6        vctrs_0.6.5        tools_4.3.2       
 [9] ps_1.7.7           generics_0.1.3     tibble_3.2.1       fansi_1.0.6       
[13] highr_0.11         pkgconfig_2.0.3    Matrix_1.6-5       SQUAREM_2021.1    
[17] RColorBrewer_1.1-3 lifecycle_1.0.4    truncnorm_1.0-9    farver_2.1.2      
[21] compiler_4.3.2     stringr_1.5.1      git2r_0.33.0       munsell_0.5.1     
[25] getPass_0.2-4      httpuv_1.6.15      htmltools_0.5.8.1  sass_0.4.9        
[29] yaml_2.3.10        later_1.3.2        pillar_1.9.0       jquerylib_0.1.4   
[33] whisker_0.4.1      cachem_1.1.0       trust_0.1-8        RSpectra_0.16-2   
[37] tidyselect_1.2.1   digest_0.6.37      stringi_1.8.4      dplyr_1.1.4       
[41] ashr_2.2-66        labeling_0.4.3     splines_4.3.2      rprojroot_2.0.4   
[45] fastmap_1.2.0      grid_4.3.2         colorspace_2.1-1   cli_3.6.3         
[49] invgamma_1.1       magrittr_2.0.3     utf8_1.2.4         withr_3.0.1       
[53] scales_1.3.0       promises_1.3.0     horseshoe_0.2.0    rmarkdown_2.28    
[57] httr_1.4.7         deconvolveR_1.2-1  evaluate_1.0.0     knitr_1.48        
[61] irlba_2.3.5.1      rlang_1.1.4        Rcpp_1.0.13        mixsqp_0.3-54     
[65] glue_1.8.0         rstudioapi_0.16.0  jsonlite_1.8.9     R6_2.5.1          
[69] fs_1.6.4

symebcovmf_tree

Annie Xie

2025-04-08

Introduction

Example

Data Generation

symEBcovMF

Progression of ELBO

Visualization of Estimate

Visualization of Fit

Visualization of Residual Matrix

Observations

symEBcovMF with refit step

Progression of ELBO

Visualization of Estimate

Visualization of Fit

Visualization of Residual Matrix

Observations