Stepping through code

When your program produces an error during execution, or executes but doesn t produce the correct answer, it is often helpful to execute the code one statement at a time and examine the values of selected variables during execution. If your procedure contains logical constructions (If or Select Case, for example), simply stepping through code will allow you to verify the logic. 

To step through the code of a Sub procedure, follow the steps in the following box. There are two ways you can begin the process. 

As you step through the code, the next statement to be executed is 

Activate a worksheet, choose Macro from the Tools menu and Macros... from the submenu. 

Activate the Visual Basic Editor. The VBA code module must be visible. 

Select the macro in the Macro Name list box and press the Step. Into button. This will display the code modulecontaiping the 

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A breakpoint allows you to halt execution at a specified line of code, rather than having to step through the code from the beginning. There are several ways to add a breakpoint ... 

When you run the macro, the code will execute until the breakpoint is reached, at which point execution will stop. You can now step through the code one statement at a time or examine the values of selected variables. 

To see the values of the selected variables or expressions, you must be in Step mode. The variables will be listed in the Watches pane (Figure 14-23), which is usually located below the Code window. The current values of the variables will be displayed as you step through the code. 

The paper is organized as follows. In Sec. 1, we introduce the main features of quantum error-correction, and, particularly, we present the already well-developed theory of quantum error-correcting codes. In Sec. 2, we present a multidimensional generalization of the quantum Zeno effect and its application to the protection of the information contained in compound systems. Moreover, we suggest a universal physical implementation of the coding and decoding steps through the non-holonomic control. Finally, in Sec. 3, we focus on the application of our method to a rubidium isotope. 

Figure 4. Coding step through the non-holonomic control technique. The two Hamiltonians Ha and Hb are alternately applied to the system during pulses whose timings are reproduced in Tab. 1. The pulsations of the laser fields involved in the coding step are represented on the spectrum of the rubidium atom.

Figure 5. Decoding step through the non-holonomic control technique. We reverse the magnetic field and the detunings of electric fields, as represented on the spectrum of the Rubidium atom, and apply the same control sequence as for coding (same timings) in the reverse way.

The subroutine MENU displays a list of mnemonics on the screen at predefined locations. In my code, these mnemonics are usually in a vertical stack, and they are all accompanied by a line of explanatory text per mnemonic. Use of the cursor keys causes a highlighted bar to step through the mnemonics. Pressing the RETURN key selects the option equivalent to the currently selected mnemonic. 

As you step through the code, the next statement to be executed is highlighted, as shown in Figure 14-18. Use the Step Into toolbutton Ji or press F8 to step through the procedure. Press F5 to run the macro from the current line. 

The listing shows the equations eoded in essentially this form exeept for the equal zero part on lines 10 through 12. The notation yp[] is used for specifying the first derivative terms in the equations. The solutions are known exponential functions of time with deeaying time eonstants of 1, 0.1 and 0.01 for the three equations respectively. The initial values of the solutions are set on line 18 and 19 to be 1.0 at zero time. The major part of the solution technique is the time loop from line 36 through line 45. For each time step the code performs the following steps ... 

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