 For instance , when one cell of a spreadsheet changes , it is necessary to recalculate the values of other cells that depend directly or indirectly on the changed cell . For this problem , the tasks to be scheduled are the recalculations of the values of individual cells of the spreadsheet . Dependencies arise when an expression in one cell uses a value from another cell . In such a case , the value that is used must be recalculated earlier than the expression that uses it . Topologically ordering the dependency graph , and using this topological order to schedule the cell updates , allows the whole spreadsheet to be updated with only a single evaluation per cell . Similar problems of task ordering arise in makefiles for program compilation and instruction scheduling for low @-@ level computer program optimization . 
 For instance , when one cell of a spreadsheet changes , it <a href='drop_aux' title='1'><mark>is</mark></a>necessary to recalculate the values of other cells <a href='null_relcl' title='2'><mark>that</mark></a>depend directly or indirectly on the changed cell . For this problem , the tasks to be scheduled <a href='drop_aux' title='3'><mark>are</mark></a>the recalculations of the values of individual cells of the spreadsheet . Dependencies arise when an expression in one cell <a href='uninflect' title='4'><mark>uses</mark></a> a value from another cell . In such a case , the value <a href='null_relcl' title='5'><mark>that</mark></a>is used must be recalculated earlier than the expression <a href='null_relcl' title='6'><mark>that</mark></a><a href='uninflect' title='7'><mark>uses</mark></a> it . Topologically ordering the dependency graph , and using this topological order to schedule the cell updates , <a href='uninflect' title='8'><mark>allows</mark></a> the whole spreadsheet to be updated with only a single evaluation per cell . Similar problems of task ordering arise in makefiles for program compilation and instruction scheduling for low @-@ level computer program optimization . 
For instance , when one cell of a spreadsheet changes , it necessary to recalculate the values of other cells depend directly or indirectly on the changed cell . For this problem , da tasks to b scheduled tdarecalculations of the values of individual cells of the spreadsheet . Dependencies arise when an expression in one cell use a value from another cell . In such a case , the value is used must be recalculated earlier than the expression use it . Topologically ordering thdaependency graph , and using this topological order to schedule the cell updates , allow thedaole spreadsheet to be updated with only a single evaluation per cell . Similar problems of task ordering arise in makefiles fir program compilation and instruction scheduling for low @-@ level computer program optimization .