I need help using the matrix function of my hp 15c. Any instruction would be much appreciated.

Lisa.
The section in the manual for Calculating With Matrices is about 41 pages. If you e-mail your address to me, I would send you a reprint.
For now, I will get you started with an example from the manual.
The 15c can work with up to 5 matrices which are named A through E using the 15's corresponding A through E keys. You can specify the size of each matrix, store and recall values of matrix elements and perform matrix operations with complex and real elements. Consider the example.

3.8x1 + 7.2x2 = 16.5
1.3x1 - 0.9x2 = -22.1 determine the values of x1 and x2.
Keystrokes:
g CF 8 deactivates complex mode.
2 Enter f DIM A dimensions matrix A to be 2X2
f Matrix 1 prepares for automatic entry of matrix elements in user mode.
f USER turns on user annunciator
3.8 STO A Denotes Matrix A row 1 column 1
7.2 STO A
1.3 STO A
.9 CHS STO A
2 ENTER 1 f DIM B Dimensions matrix B to be 2X1
16.5 STO B
22.1 CHS STO B
f RESULT C designates matrix C storing the result.
RCL MATRIX B
RCL MATRIX A
/ press divide key
RCL C displays 1, 1 (row 1, column 1)
-11.2887 (value of (X1))
RCL C 8.2496 (value of (X2))
f USER deactivates user mode
f MATRIX 0 Clears all matrices.

The solution to the system is X1 = -11.2887 ans X2 = 8.2496.
Up to 64 matrix elements can be stored in memory. Use all 64 in one matrix or distribute them among up to 5 matrices. Matrix inversion can be performed on an 8X8 with real elements or a 4X4 with complex elements.
If you have need of further help, I suggest you e-mail me directly at wldrylie@702com.net. I will help more. Or e-mail mailing address, I will send you 15C reprint of matrix section of manual. Good luck. I still have fun using my 15C at work. I can also provide many an engineering example from my daily work and programs. Let me know.
Bill.

I have an out-of-production HP15C, but I have misplaced the basic user's manual, although I have the advanced manual. There is an annoying "c" indicator on the lower level of the window and slightly more than three-quaters to the right. I have a guess as to think that it indicates "complex" mode. But when I when I hit the "Re><Im" button, nothing happens to the "c." Can someone help me? Thanks.

you're right, it is in complex mode.

to deactivate complex mode, clear flag 8 (g CF 8).

Yes, SF 8 activates complex mode and CG 8 desactivates it.

Another amazing sutff with the flags is SF 9 activates flashing display and CF 9 desactivates it...

Hi Thibaut. Still busy?