reshape_expr(expr, new_dim)

x <- Variable(4)
mat <- cbind(c(1,-1), c(2,-2))
vec <- matrix(1:4)
expr <- reshape_expr(x,c(2,2))
obj <- Minimize(sum(mat %*% expr))
prob <- Problem(obj, list(x == vec))
result <- solve(prob)
result$value

A <- Variable(2,2)
c <- 1:4
expr <- reshape_expr(A,c(4,1))
obj <- Minimize(t(expr) %*% c)
constraints <- list(A == cbind(c(-1,-2), c(3,4)))
prob <- Problem(obj, constraints)
result <- solve(prob)
result$value
result$getValue(expr)
result$getValue(reshape_expr(expr,c(2,2)))

C <- Variable(3,2)
expr <- reshape_expr(C,c(2,3))
mat <- rbind(c(1,-1), c(2,-2))
C_mat <- rbind(c(1,4), c(2,5), c(3,6))
obj <- Minimize(sum(mat %*% expr))
prob <- Problem(obj, list(C == C_mat))
result <- solve(prob)
result$value
result$getValue(expr)

a <- Variable()
c <- cbind(c(1,-1), c(2,-2))
expr <- reshape_expr(c * a,c(1,4))
obj <- Minimize(expr %*% (1:4))
prob <- Problem(obj, list(a == 2))
result <- solve(prob)
result$value
result$getValue(expr)

expr <- reshape_expr(c * a,c(4,1))
obj <- Minimize(t(expr) %*% (1:4))
prob <- Problem(obj, list(a == 2))
result <- solve(prob)
result$value
result$getValue(expr)