Loops with Input

Loops become very powerful when combined with input statements. Consider this simple example  

This script prints out the prompt Type something and immediately enters a while loop. The while loop here is a little different from the ones shown before. Instead of doing a comparison, the while loop s test contains the expression defined ( line = ). This expression looks a bit bizarre but can be explained very simply. The first thing that happens is that a line of input is read and assigned to the variable line. Then, line is then passed to a new function named defined, which returns true if the contents of a variable are defined, false otherwise. Recall that reads lines from a file (or keyboard) until it reaches the end of the file, at which point it returns undefined. This test is telling the while loop to read input lines one at a time imtil the end of the file is reached. The parentheses ensine that defined is called after the line is read into line, not before. 

For each line read in this way, the while loop executes three statements. The first statement calls chomp to remove the newline character from the end of line. The second statement uses variable interpolation to insert the input line into the string You typed line n n and then prints the resulting string out. The last statement displays the prompt again. The result looks like this  

Because it can be inconvenient to remember obscure control characters, the program can be made a bit friendlier by allowing the user to type quit to exit the loop  

The main change is the line that immediately follows the chomp. This introduces a new function named last, which acts as a loop modifier. It is only allowed to occur within the body of a loop. When executed, last causes the script to exit the loop immediately, even though the loop test may still be true. This statement compares the contents of line to the string quit. If they match, the last function is executed and the loop finishes. Ruiming fhe program now, entering the word quit exits the loop so that the last line (which prints goodbye ) can be executed. 

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Pumping, Velocity Head, and Power. Mechanical mixers can be compared with pumps (1) because they produce circulating capacity and velocity head H. The analogy between a pump and mixer can be appreciated by comparing a pumping loop with a mixing tank (Fig. 2). Power input P to a pump is represented by... 

Figure 8.16 shows a portion of typical N, l)-net. The arrows indicate inputs to given sites and + and represent the two active Boolean functions at the sites toward which the arrows are pointing. Note that the structure degenerates into subnets of dynamically independent loops with outwmdly radiating tails . An input signal cannot enter a loop since the site by which it would enter the loop... 

First, assume that for each w the computation actually left W with tail y z v for y a nonempty substring of yw. Now take our new z = az. For any w in (a,b +, the computation with input (e,yw z v) leaves loop W by hypothesis with tail y z v for y some nonempty terminal substring of yw a since y is nonempty, y = y"a and so the tail is y"z v for y" some terminal substring of yw. This settles this case. 

Diltiazem Functional relationship between PK and PD parameters is described by hysteresis loops with a clockwise rotation. This cannot be explained in the classical way by the time lag between central and effect compartments. The model of down regulation/toler-ance development is proposed as a result supported by the finding that the shape of the hysteresis is dependent on the absorption rate of diltiazem, calculated as mean input time. Acute tolerance to dilitazem develops at least with the electrophysiologi-cal action of diltiazem after oral application and that the extent of tolerance development increases when decreasing its absorption rate. Bioequivalence assessment of diltiazem is possible using PD parameters however, because PK/PD relationships are influenced by the absorption rate, extent parameters may be misinterpreted when rate parameters of the test formulations are different... 

For example, a typical billion Ib/yr ethylene plant may have 600 control loops with control valves and 400 interacting loops with a cost of about 6 million. (Skrokov. 1980. pp. 13, 49 see Sec. 3.1) the computer implementation of this control system will cost another 3 million. Figure 3.1 shows the control system of an ethylene fractionator which has 12 input signals to the computer and four outgoing reset signals to flow controllers. 

Mangan, S. Zaslaver, A. Alon, U. The coherent feedforward loop serves as a sign-sensitive delay element in transcription networks. J Mol Biol 2003, 334 197-204. Kalir, S. Mangan, S. Alon, U. A coherent feed-forward loop with a S UM input function prolongs flagella expression in Escherichia coli. Mol Syst Biol 2005, 1 2005-2006. 

The concentration of impurities (present in the feed) in the process evolves over a very slow horizon (days or, possibly, weeks). Moreover, the presence of impurities in the feed stream, together with significant material recycling, can lead to the accumulation of impurities in the recycle loop, with detrimental effects on the operation of the process and on its economics (Baldea et al. 2006). Therefore, as was shown in Chapter 4, the control of the impurity levels in the process is an important operational objective, and, according to the analysis presented above, it should be addressed in the slow time scale, using the flow rate of the purge stream, up, as a manipulated input. 

Use for construct when the number of loop iterations is known beforehand. Likewise, use while construct when the number of loop iterations is not known beforehand. Cases include reading data from a file or from user input line by line until the end is encountered. Though this can be achieved by using a for loop with a conditional break statement, the while statement conveys the logic clearly. Some special cases require using do-while (when the first statement has to be executed before the conditional). 

The stability criterion stated above secures stable response of a feedback system independently if the input changes are in the set point or the load. The reason is that the roots of the characteristic equation are the common poles of the two transfer functions, GSp and Gioad, which determine the stability of the closed loop with respect to changes in the set point and the load, respectively. 

The relative-gain array indicates how the inputs should be coupled with the outputs to form loops with the smaller amount of interaction. But the persisting interaction, although it is the smallest possible, may not be small enough. Example 24.5 demonstrated this aspect clearly. In such a case, the two control loops still affect each other s operation very seriously, and the overall control system is characterized as unacceptable. 

VI.14 Consider the processes with input-output relationships given in Problem VI.12. Using Bristol s relative-gain array, select the loops with the minimum steady-state interaction. 

The continuous models (e.g., differential equations in the time domain, or input-output models in the Laplace domain) are not convenient to use to analyze the dynamic behavior of loops with computer control discrete-time models are needed. 

VI. 16 Select the control loops with minimum steady-state interaction for the following system with two outputs and three inputs ... 

The Laplace transforms allowed us to develop simple input-output relationships for a process and provided the framework for easy analysis and design of loops with continuous analog controllers. For discrete-time systems we need to introduce new analytical tools. These will be provided by the z-transforms. 

Figure 29.1 Components of a DDC loop with discrete-time inputs and outputs.

In the preceding section the analysis was centered around the response of the discrete components in a direct digital control (DDC) loop with characteristic representative the control algorithm. The use of z-transforms allowed easy and straightforward development of simple input-output models through the discrete transfer functions. 

Figure 11.5. Partial output from a PHDtopology prediction. The input sequence is pendrin, which is responsible for Pendred syndrome (Everett et al., 1998). The row labeled aa shows a portion of the input sequence, and the row labeled Rel htm gives the reliability index of prediction at each position of the protein values range from 0 to 9, with 9 representing the maximum possible confidence for the assignment at that position. The last line, labeled PHDThm, contains one of three letters a T represents a transmembrane region, whereas an i or o represents the orientation of the loop with respect to the membrane (inside or outside).

Figure 14.6 Conceptual implementation of lock-in amplification, comprising the signal channel with input amplifier and band-pass filter, the reference channel with phase-locked loop (PLL)-reference generator and continuous phase shifter, the PSD, andthe output channel with low-pass filter and buffer amplifier...

Draw the symbol for any type of op-amp, labelling the input(s), output, power, and ground. Include both a positive and a negative feedback loop, with resistors (but no numbers are needed). 

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