Alternative Equation Formats

$${\displaystyle y=\{\begin{array}{ll}\frac{1}{2}(x_i+x_{i+1})& \text{if}{\displaystyle \underset{j=1}{\overset{i}{\sum <!--\; \sum \; -->}}{w}_j=pW}\\ x_{i+1}& \text{if}{\displaystyle \underset{j=1}{\overset{i}{\sum <!--\; \sum \; -->}}{w}_j<pW<{\displaystyle \underset{j=1}{\overset{i+1}{\sum <!--\; \sum \; -->}}{w}_j}}\end{array}}$$

$${\displaystyle y=\{\begin{array}{ll}\frac{1}{2}(x_i+x_{i+1})& \text{if}{\displaystyle \underset{j=1}{\overset{i}{\sum <!--\; \sum \; -->}}{w}_j=pW}\\ x_{i+1}& \text{if}{\displaystyle \underset{j=1}{\overset{i}{\sum <!--\; \sum \; -->}}{w}_j<pW<{\displaystyle \underset{j=1}{\overset{i+1}{\sum <!--\; \sum \; -->}}{w}_j}}\end{array}}$$

\[ y = \begin{cases} \frac{1}{2} \left( x_ i + x_{i+1} \right) & \mbox{if} \displaystyle \sum _{j=1}^ i w_ j = pW \\ x_{i+1} & \mbox{if} \displaystyle \sum _{j=1}^ i w_ j < pW < \displaystyle \sum _{j=1}^{i+1} w_ j \end{cases} \]