28 



MULTIPLE PURPOSE RIVER DEVELOPMENT 



FIGURE 4, The Production Function 



is called the marginal input, and this is seen to be the reciprocal of 

 the input-output relationship which defines marginal productivity. 

 It is apparent from Figure 5 that, if the input of factor Y is held 

 constant, beyond a certain point within the range of diminishing 

 marginal productivity, increasingly larger marginal inputs of X 

 are required to raise output by an additional unit. The concept of 

 the diminishing marginal productivity of a factor can perhaps be 

 made clearer by a concrete example. Let us employ the farm enter- 

 prise again, but this time assume that all factors other than water 

 are held constant and increase in production is sought solely by 



