eyeball. 1  Photoreceptors are the cells in the retina that respond to light. Their distinguishing feature is the presence of large amounts of tightly packed membrane that contains the photopigment rhodopsin or a related molecule.
In chemical analysis,  matrix refers to the components of a sample other than the analyte of interest. The matrix can have a considerable effect on the way the analysis is conducted and the quality of the results obtained; such effects are called matrix effects. For example, the ionic strength of the solution can have an effect on the activity coefficients of the analytes.
Defining MatricesÂ¶. Defining a matrix is similar to defining a vector (Introduction to Vectors in Matlab). To define a matrix, you can treat it like a column of row vectors (note that the spaces are required!): >> A = [ 1 2 3; 3 4 5; 6 7 8] A = 1 2 3 3 4 5 6 7 8.