The ornamental design for a matrixclock, as shown and described.
FIG. 1 is a front elevational view of a matrix clock showing our new design;
FIG. 2 is a second front elevational view of our design of FIG. 1; and,
FIG. 3 is a third front elevational view of the design of FIG. 1.
The base structure in FIG. 1, the building structure in FIG. 2, and the pedestal structure in FIG. 3, depicted by broken lines, have been shown for the purpose of illustrating environment that forms no part of the claimed design.