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Dynamic Programming



Dynamic programming is both a mathematical optimization method and a computer programming method. The method was developed by Richard Bellman in the 1950s and has found applications in numerous fields, from aerospace engineering to economics.




Dynamic Programming



If sub-problems can be nested recursively inside larger problems, so that dynamic programming methods are applicable, then there is a relation between the value of the larger problem and the values of the sub-problems.[1] In the optimization literature this relationship is called the Bellman equation.


There are two key attributes that a problem must have in order for dynamic programming to be applicable: optimal substructure and overlapping sub-problems. If a problem can be solved by combining optimal solutions to non-overlapping sub-problems, the strategy is called "divide and conquer" instead.[1] This is why merge sort and quick sort are not classified as dynamic programming problems.


Some programming languages can automatically memoize the result of a function call with a particular set of arguments, in order to speed up call-by-name evaluation (this mechanism is referred to as call-by-need). Some languages make it possible portably (e.g. Scheme, Common Lisp, Perl or D). Some languages have automatic memoization built in, such as tabled Prolog and J, which supports memoization with the M. adverb.[4] In any case, this is only possible for a referentially transparent function. Memoization is also encountered as an easily accessible design pattern within term-rewrite based languages such as Wolfram Language.


Dynamic programming is widely used in bioinformatics for tasks such as sequence alignment, protein folding, RNA structure prediction and protein-DNA binding. The first dynamic programming algorithms for protein-DNA binding were developed in the 1970s independently by Charles DeLisi in USA[5] and Georgii Gurskii and Alexander Zasedatelev in USSR.[6] Recently these algorithms have become very popular in bioinformatics and computational biology, particularly in the studies of nucleosome positioning and transcription factor binding.


From a dynamic programming point of view, Dijkstra's algorithm for the shortest path problem is a successive approximation scheme that solves the dynamic programming functional equation for the shortest path problem by the Reaching method.[7][8][9]


Using dynamic programming in the calculation of the nth member of the Fibonacci sequence improves its performance greatly. Here is a naïve implementation, based directly on the mathematical definition:


In genetics, sequence alignment is an important application where dynamic programming is essential.[11] Typically, the problem consists of transforming one sequence into another using edit operations that replace, insert, or remove an element. Each operation has an associated cost, and the goal is to find the sequence of edits with the lowest total cost.


Matrix chain multiplication is a well-known example that demonstrates utility of dynamic programming. For example, engineering applications often have to multiply a chain of matrices. It is not surprising to find matrices of large dimensions, for example 100100. Therefore, our task is to multiply matrices A 1 , A 2 , . . . . A n \displaystyle A_1,A_2,....A_n . Matrix multiplication is not commutative, but is associative; and we can multiply only two matrices at a time. So, we can multiply this chain of matrices in many different ways, for example:


At this point, we have several choices, one of which is to design a dynamic programming algorithm that will split the problem into overlapping problems and calculate the optimal arrangement of parenthesis. The dynamic programming solution is presented below.


The term dynamic programming was originally used in the 1940s by Richard Bellman to describe the process of solving problems where one needs to find the best decisions one after another. By 1953, he refined this to the modern meaning, referring specifically to nesting smaller decision problems inside larger decisions,[16] and the field was thereafter recognized by the IEEE as a systems analysis and engineering topic. Bellman's contribution is remembered in the name of the Bellman equation, a central result of dynamic programming which restates an optimization problem in recursive form.


The word dynamic was chosen by Bellman to capture the time-varying aspect of the problems, and because it sounded impressive.[11] The word programming referred to the use of the method to find an optimal program, in the sense of a military schedule for training or logistics. This usage is the same as that in the phrases linear programming and mathematical programming, a synonym for mathematical optimization.[17]


The above explanation of the origin of the term is lacking. As Russell and Norvig in their book have written, referring to the above story: "This cannot be strictly true, because his first paper using the term (Bellman, 1952) appeared before Wilson became Secretary of Defense in 1953."[18] Also, there is a comment in a speech by Harold J. Kushner, where he remembers Bellman. Quoting Kushner as he speaks of Bellman: "On the other hand, when I asked him the same question, he replied that he was trying to upstage Dantzig's linear programming by adding dynamic. Perhaps both motivations were true."


If any problem can be divided into subproblems, which in turn are divided into smaller subproblems, and if there are overlapping among these subproblems, then the solutions to these subproblems can be saved for future reference. In this way, efficiency of the CPU can be enhanced. This method of solving a solution is referred to as dynamic programming.


Dynamic programming by memoization is a top-down approach to dynamic programming. By reversing the direction in which the algorithm works i.e. by starting from the base case and working towards the solution, we can also implement dynamic programming in a bottom-up manner.


Richard Bellman was the one who came up with the idea for dynamic programming in the 1950s. It is a method of mathematical optimization as well as a methodology for computer programming. It applies to issues one can break down into either overlapping subproblems or optimum substructures.


For example, when using the dynamic programming technique to figure out all possible results from a set of numbers, the first time the results are calculated, they are saved and put into the equation later instead of being calculated again. So, when dealing with long, complicated equations and processes, it saves time and makes solutions faster by doing less work.


The dynamic programming algorithm tries to find the shortest way to a solution when solving a problem. It does this by going from the top down or the bottom up. The top-down method solves equations by breaking them into smaller ones and reusing the answers when needed. The bottom-up approach solves equations by breaking them up into smaller ones, then tries to solve the equation with the smallest mathematical value, and then works its way up to the equation with the biggest value.


Using dynamic programming to solve problems is more effective than just trying things until they work. But it only helps with problems that one can break up into smaller equations that will be used again at some point.


Meanwhile, dynamic programming is an optimization technique for recursive solutions. It is the preferred technique for solving recursive functions that make repeated calls to the same inputs. A function is known as recursive if it calls itself during execution. This process can repeat itself several times before the solution is computed and can repeat forever if it lacks a base case to enable it to fulfill its computation and stop the execution.


However, not all problems that use recursion can be solved by dynamic programming. Unless solutions to the subproblems overlap, a recursion solution can only be arrived at using a divide-and-conquer method.


Dynamic programming is used when one can break a problem into more minor issues that they can break down even further, into even more minor problems. Additionally, these subproblems have overlapped. That is, they require previously calculated values to be recomputed. With dynamic programming, the computed values are stored, thus reducing the need for repeated calculations and saving time and providing faster solutions.


Dynamic programming works by breaking down complex problems into simpler subproblems. Then, finding optimal solutions to these subproblems. Memorization is a method that saves the outcomes of these processes so that the corresponding answers do not need to be computed when they are later needed. Saving solutions save time on the computation of subproblems that have already been encountered.


Therefore, when solving an LCS problem, it is more efficient to use a dynamic algorithm than a recursive algorithm. Dynamic programming stores the results of each function call so that it can be used in future calls, thus minimizing the need for redundant calls.


When dynamic programming algorithms are executed, they solve a problem by segmenting it into smaller parts until a solution arrives. They perform these tasks by finding the shortest path. Some of the primary dynamic programming algorithms in use are:


An example of dynamic programming algorithms, greedy algorithms are also optimization tools. The method solves a challenge by searching for optimum solutions to the subproblems and combining the findings of these subproblems to get the most optimal answer.


The Floyd-Warshall method uses a technique of dynamic programming to locate the shortest pathways. It determines the shortest route across all pairings of vertices in a graph with weights. Both directed and undirected weighted graphs can use it.


Some recursive functions are invoked three times in the recursion technique, indicating the overlapping subproblem characteristic required to calculate issues that use the dynamic programming methodology. 041b061a72


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