Last updated: 2025-10-22

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Rmd 26200cc Matthew Stephens 2025-10-22 workflowr::wflow_publish("fastica_01.Rmd")

library(fastICA)
library(flashier)
Loading required package: ebnm
library(RcppHungarian)

Introduction

I wanted to take a look at the fastICA package and try it out on a simple simulation. This simulation is based on using a mixture of two Gaussians (a “spike-and-slab” prior) for the latent factors, as in https://github.com/daniel-lazarev/GUIDE/blob/main/GUIDE-simulation.ipynb.

M <- 10000 # Number of variants/samples (rows)
L <- 10    # True number of latent factors
T <- 100   # Number of traits/phenotypes (columns)

s_1 <- 1   # Standard Deviation 1 (Spike component)
s_2 <- 5   # Standard Deviation 2 (Slab component)
eps <- 1e-2 # Standard Deviation for observation noise 

# Set seed for reproducibility
set.seed(42)

# Data Simulation (G = X %*% Y + noise)

# 3.1. Generating Standard Deviation Matrices (a and b)
# Elements are sampled from {s_1, s_2} [1, 2].
sd_choices <- c(s_1, s_2)

# Matrix 'a' (M x L): Standard deviations for X (Probabilities p=[0.7, 0.3]) [4]
p_a <- c(0.7, 0.3)
a_vector <- sample(sd_choices, size = M * L, replace = TRUE, prob = p_a)
a <- matrix(a_vector, nrow = M, ncol = L)

# Matrix 'b' (L x T): Standard deviations for Y (Probabilities p=[0.8, 0.2]) [4]
p_b <- c(0.8, 0.2)
b_vector <- sample(sd_choices, size = L * T, replace = TRUE, prob = p_b)
b <- matrix(b_vector, nrow = L, ncol = T)

# Generating Latent Factors (X and Y)
# X is drawn from Normal(0, a)
X <- matrix(rnorm(M * L, mean = 0, sd = a), nrow = M, ncol = L)

# Y is drawn from Normal(0, b)
Y <- matrix(rnorm(L * T, mean = 0, sd = b), nrow = L, ncol = T)

# Generating Noise and Final Data Matrix G
# Noise is generated from Normal(0, eps)
noise <- matrix(rnorm(M * T, mean = 0, sd = eps), nrow = M, ncol = T)

# Calculate the final data matrix G = X @ Y + noise
G <- X %*% Y + noise

Now I’ll apply fastICA to this matrix. It produces a factorization X = SA where S are the sources (independent components) which are designed to be as “non-gaussian” as possible. In this case we see ICA finds all of the components essentially perfectly.

ica_result <- fastICA(G, n.comp = 10)
cormat <- cor(ica_result$S,X)

apply(abs(cormat),1, max)
 [1] 0.9996204 0.9998202 0.9998590 0.9998774 0.9998719 0.9997143 0.9997914
 [8] 0.9997270 0.9997739 0.9998257
assignment_problem <- RcppHungarian::HungarianSolver(-1*abs(cormat))
pairings <- assignment_problem$pairs
image(abs(cormat)[pairings[,1], pairings[,2]])

Compare with flashier: we see flashier is much less effective at recovering the components here.

f1 = flash(G, greedy_Kmax = 20, ebnm_fn = ebnm_point_laplace, backfit=TRUE)
Adding factor 1 to flash object...
Adding factor 2 to flash object...
Adding factor 3 to flash object...
Adding factor 4 to flash object...
Adding factor 5 to flash object...
Adding factor 6 to flash object...
Adding factor 7 to flash object...
Adding factor 8 to flash object...
Adding factor 9 to flash object...
Adding factor 10 to flash object...
Adding factor 11 to flash object...
Factor doesn't significantly increase objective and won't be added.
Wrapping up...
Done.
Backfitting 10 factors (tolerance: 1.49e-02)...
  Difference between iterations is within 1.0e+06...
  Difference between iterations is within 1.0e+05...
  Difference between iterations is within 1.0e+04...
  Difference between iterations is within 1.0e+03...
  Difference between iterations is within 1.0e+02...
Wrapping up...
Done.
Nullchecking 10 factors...
Done.
cormat <- cor(f1$L_pm,X)

apply(abs(cormat),1, max)
 [1] 0.6180761 0.6401523 0.5992492 0.5850770 0.5961263 0.5756047 0.7152306
 [8] 0.6701436 0.9302887 0.9153016
assignment_problem <- RcppHungarian::HungarianSolver(-1*abs(cormat))
pairings <- assignment_problem$pairs
image(abs(cormat)[pairings[,1], pairings[,2]])

One question is whether this is because of flashier converging to a local optimum. To assess this we initialize it to the ica solution. We see that this initialization produces essentially the same results as ICA (ie it does not move away from the correct answer) and produces a better elbo than the greedy fit.

f2 = flash_init(G) |> flash_factors_init(init = list(ica_result$S,t(ica_result$A)), ebnm_fn = ebnm_point_laplace) |> flash_backfit()
Backfitting 10 factors (tolerance: 1.49e-02)...
  Difference between iterations is within 1.0e+06...
  Difference between iterations is within 1.0e+05...
  Difference between iterations is within 1.0e+04...
  Difference between iterations is within 1.0e+03...
  Difference between iterations is within 1.0e+02...
  Difference between iterations is within 1.0e+01...
  Difference between iterations is within 1.0e+00...
  Difference between iterations is within 1.0e-01...
  Difference between iterations is within 1.0e-02...
Wrapping up...
Done.
cormat <- cor(f2$L_pm,X)

apply(abs(cormat),1, max)
 [1] 0.9996207 0.9998206 0.9998595 0.9998766 0.9998720 0.9997154 0.9997887
 [8] 0.9997271 0.9997747 0.9998256
assignment_problem <- RcppHungarian::HungarianSolver(-1*abs(cormat))
pairings <- assignment_problem$pairs
image(abs(cormat)[pairings[,1], pairings[,2]])

f1$elbo
[1] 2302730
f2$elbo
[1] 2317773

ICA with sequential fit

One feature of fastICA fit is that by default it fits all components jointly. Here I try the sequential (“deflation”) method. Interestingly it also finds the exact solution.

ica_result2 <- fastICA(G, n.comp = 10, alg.typ="deflation")
cormat <- cor(ica_result2$S,X)

apply(abs(cormat),1, max)
 [1] 0.9997359 0.9996179 0.9997392 0.9997450 0.9995758 0.9996718 0.9994287
 [8] 0.9995173 0.9986505 0.9997183
assignment_problem <- RcppHungarian::HungarianSolver(-1*abs(cormat))
pairings <- assignment_problem$pairs
image(abs(cormat)[pairings[,1], pairings[,2]])

ICA with fewer components

Interestingly, if you just extract a few components, ICA does much less well. I think this is because ICA has an inital step that projects onto the first n.comp PCs, so if you use, say, n.comp = 2 it only keeps information in the first 2 PCs, so it can’t find the true directions.

ica_result3 <- fastICA(G, n.comp = 2)
cormat <- cor(ica_result3$S,X)
apply(abs(cormat),1, max)
[1] 0.5856762 0.7153216

ICA with too many components

On the other hand, using too many components, the algorithm is robust.

ica_result4 <- fastICA(G, n.comp = 20)
cormat <- cor(ica_result4$S,X)
apply(abs(cormat),2, max)
 [1] 0.9995374 0.9997505 0.9995204 0.9995720 0.9993905 0.9993869 0.9992612
 [8] 0.9994589 0.9996332 0.9994735
assignment_problem <- RcppHungarian::HungarianSolver(-1*abs(cormat))
pairings <- assignment_problem$pairs
image(abs(cormat)[pairings[,1], pairings[,2]])

ICA with all components

Even using all the components, the algorithm is robust.

ica_result5 <- fastICA(G, n.comp = 100)
cormat <- cor(ica_result5$S,X)
apply(abs(cormat),2, max)
 [1] 0.9972462 0.9967769 0.9955027 0.9974634 0.9957685 0.9957966 0.9956086
 [8] 0.9952900 0.9968206 0.9961997
assignment_problem <- RcppHungarian::HungarianSolver(-1*abs(cormat))
pairings <- assignment_problem$pairs
image(abs(cormat)[pairings[,1], pairings[,2]])

ICA with all components and sequential

Here we use all the components, together with the deflation algorithm. This is maybe the most similar algorithm to the greedy approach in flashier. Interestingly this takes by far the longest time of all the ICA runs we made here. However, it does successfully extract all the components.

ica_result6 <- fastICA(G, n.comp = 100, alg.typ="deflation")
cormat <- cor(ica_result6$S,X)
apply(abs(cormat),2, max)
 [1] 0.9977926 0.9978682 0.9972768 0.9977222 0.9971092 0.9970703 0.9973687
 [8] 0.9963451 0.9972798 0.9972659
assignment_problem <- RcppHungarian::HungarianSolver(-1*abs(cormat))
pairings <- assignment_problem$pairs
image(abs(cormat)[pairings[,1], pairings[,2]])


sessionInfo()
R version 4.4.2 (2024-10-31)
Platform: aarch64-apple-darwin20
Running under: macOS Sequoia 15.6.1

Matrix products: default
BLAS:   /Library/Frameworks/R.framework/Versions/4.4-arm64/Resources/lib/libRblas.0.dylib 
LAPACK: /Library/Frameworks/R.framework/Versions/4.4-arm64/Resources/lib/libRlapack.dylib;  LAPACK version 3.12.0

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: Europe/London
tzcode source: internal

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

other attached packages:
[1] RcppHungarian_0.3 flashier_1.0.56   ebnm_1.1-34       fastICA_1.2-7    

loaded via a namespace (and not attached):
 [1] softImpute_1.4-3     gtable_0.3.6         xfun_0.52           
 [4] bslib_0.9.0          ggplot2_3.5.2        htmlwidgets_1.6.4   
 [7] ggrepel_0.9.6        lattice_0.22-6       quadprog_1.5-8      
[10] vctrs_0.6.5          tools_4.4.2          generics_0.1.4      
[13] parallel_4.4.2       Polychrome_1.5.4     tibble_3.3.0        
[16] pkgconfig_2.0.3      Matrix_1.7-2         data.table_1.17.6   
[19] SQUAREM_2021.1       RColorBrewer_1.1-3   RcppParallel_5.1.10 
[22] scatterplot3d_0.3-44 lifecycle_1.0.4      truncnorm_1.0-9     
[25] compiler_4.4.2       farver_2.1.2         stringr_1.5.1       
[28] git2r_0.35.0         progress_1.2.3       RhpcBLASctl_0.23-42 
[31] httpuv_1.6.15        htmltools_0.5.8.1    sass_0.4.10         
[34] lazyeval_0.2.2       yaml_2.3.10          plotly_4.11.0       
[37] crayon_1.5.3         tidyr_1.3.1          later_1.4.2         
[40] pillar_1.10.2        jquerylib_0.1.4      whisker_0.4.1       
[43] uwot_0.2.3           cachem_1.1.0         trust_0.1-8         
[46] gtools_3.9.5         tidyselect_1.2.1     digest_0.6.37       
[49] Rtsne_0.17           stringi_1.8.7        purrr_1.0.4         
[52] dplyr_1.1.4          ashr_2.2-66          splines_4.4.2       
[55] cowplot_1.1.3        rprojroot_2.0.4      fastmap_1.2.0       
[58] grid_4.4.2           colorspace_2.1-1     cli_3.6.5           
[61] invgamma_1.1         magrittr_2.0.3       prettyunits_1.2.0   
[64] scales_1.4.0         promises_1.3.3       horseshoe_0.2.0     
[67] httr_1.4.7           rmarkdown_2.29       fastTopics_0.7-07   
[70] deconvolveR_1.2-1    workflowr_1.7.1      hms_1.1.3           
[73] pbapply_1.7-2        evaluate_1.0.4       knitr_1.50          
[76] viridisLite_0.4.2    irlba_2.3.5.1        rlang_1.1.6         
[79] Rcpp_1.0.14          mixsqp_0.3-54        glue_1.8.0          
[82] rstudioapi_0.17.1    jsonlite_2.0.0       R6_2.6.1            
[85] fs_1.6.6