Function initializes a named list with a unique member so-called "expressionmatrix" containing the input gene expression matrix. Genes with a variance equal to zero are filtered out from the gene expression matrix at this step.
A numeric matrix representing a gene expression matrix gathering the normalized expression levels of each single-cell in the experiment (displayed by columns) for each detected gene (displayed by rows).
a named list: list(expressionmatrix=BaseData)
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